Goalflashes and major incidents:
3-1 to Liverpool Ferdinand's penalty is saved by Jose Reina and it is Liverpool who celebrate winning the 125th FA Cup. Reina has saved three of West Ham's four penalties, and the Hammers are understandably distraught.
3-1 to Liverpool John Arne Riise goes down the middle but Shaka Hislop has already dived out of the way. Anton Ferdinand must now score for the Hammers.
2-1 to Liverpool Paul Konchesky's poor penalty down the middle is easily kept out by Jose Reina.
2-1 to Liverpool Steven Gerrard confidently puts the Reds ahead again as Shaka Hislop goes the wrong way.
1-1 It's all square as Teddy Sheringham lashes in for West Ham.
1-0 to Liverpool Shaka Hislop responds by guessing right and saving Sami Hyypia's weak effort.
1-0 to Liverpool Jose Reina dives low to his right to Bobby Zamora's effort.
1-0 to Liverpool Dietmar Hamann stutters before blasting high to Shaka Hislop's right.
Liverpool will take the first penalty - at the West Ham end.
There's so much pressure on the individual with penalties. That's why I never took one
BBC Sport's Alan Hansen
FULL-TIME: This incredible FA Cup final will be decided by penalties.
90 mins (+ 29): The drama continues to the death...Jose Reina turns Nigel Reo-Coker's header onto the post and from the rebound, the hobbling Marlon Harewood hooks wide.
90 mins (+ 27): Liverpool look to be building towards one last attack as penalties loom.
90 mins (+ 25): Bobby Zamora is the quickest man on the pitch and he runs through virtually the entire Liverpool defence before Sami Hyypia brings him down. Yossi Benayoun's free-kick comes back off the wall.
90 mins (+ 23): Marlon Harewood attempts to come back on for West Ham but he is unable to put any weight on his right foot and is quickly off again.
90 mins (+ 21): It's very hard to keep track of which Liverpool players are on their feet. Gerrard, Sissoko and Finnan go down in quick suuccession. And now West Ham striker Marlon Harewood joins in the fun, although his problem seems to be an injury rather than cramp.
90 mins (+ 19): Bobby Zamora wins a corner for West Ham but it comes to nothing as referee Alan Wiley spots a foul on Liverpool keeper Jose Reina.
90 mins (+ 17): Liverpool are effectively down to 10 men with Djibril Cisse little more than a spectator.
90 mins (+ 16): Jan Kronkamp attacks down the right for Liverpool but it's hard to tell if the end result is a shot or a cross. Either way, it goes harmlessly behind.
90 mins (+ 16): The second half of extra-time is under way.
HALF-TIME: Liverpool's cramp count continues to rise. Momo Sissoko joins Djibril Cisse, Steve Finnan and Jamie Carragher on the struggling list. Cisse now has a hamstring injury as well which is rapidly strapped by the Liverpool trainer.
90 mins (+ 14): Sami Hyypia has the Liverpool fans purring with an unlikely piece of skill in midfield before arrowing a shot just wide.
90 mins (+ 9): It's another Liverpool corner and as West Ham hesitate, the ball arrives at Djibril Cisse's feet but the unmarked striker cannot control it.
90 mins (+ 7): Liverpool win a corner. Steven Gerrard wanders over to take it and from the clearance, John Arne Riise's swerving strike whistles over the bar.
90 mins (+ 4): Not surprisingly, it's a slow start to the added period. Jamie Carragher is the latest Liverpool player to succumb to cramp.
EXTRA-TIME: Liverpool get extra-time under way.
West Ham deserved to win. They were the better side but unfortunately for them, Liverpool have got a player called Steven Gerrard
BBC Sport's Alan Hansen
FULL-TIME: Time to draw breath as normal time comes to an end. West Ham's players look fitter than their Liverpool counterparts - but they must be mentally shattered after Gerrard's late stunner.
93 mins: Liverpool's players are dropping like flies. Steve Finnan is the latest to hobble off with cramp. Rafa Benitez has used up all his substitutions.
90 mins: GOAL Liverpool 3-3 West Ham
The clock hits 90 minutes and Steven Gerrard rifles in a cracking volley from 30 yards. Extra time beckons as the BBC's John Motson ponders: "Is this the best FA Cup final in history?"
86 mins: Teddy Sheringham's first contribution is to give away a free-kick for handball. Steven Gerrard, who is still limping, blasts his effort hopelessly high and wide.
85 mins: Veteran West Ham striker Teddy Sheringham is on for Matthew Etherington.
84 mins: Worrying scenes for Liverpool and England fans as Steven Gerrard hobbles about in his own half. It is unclear whether it is cramp or an injury.
81 mins: Into the last 10 minutes and Fernando Morientes heads over for an increasingly desperate Liverpool. Nigel Reo-Coker is the Hammers' hero now as he shadows Liverpool skipper and most likely saviour Steven Gerrard.
77 mins: Liverpool are seeing plenty of the ball but aren't troubling West Ham keeper Shaka Hislop. Alan Pardew responds to the situation by bringing on defender Christian Dailly for midfielder Carl Fletcher.
70 mins: West Ham skipper Nigel Reo-Coker cuts inside and plants his shot narrowly over the bar. Dean Ashton's excellent afternoon comes to an end as he is replaced by Bobby Zamora. Liverpool take off striker Peter Crouch and send on Dietmar Hamann.
67 mins: Liverpool's Xabi Alonso, an injury doubt until just before the game, comes off to be replaced by Jan Kronkamp. It just doesn't seem to be Liverpool's afternoon.
64 mins: GOAL Liverpool 2-3 West Ham
This extraordinary final takes yet another twist as Paul Konchesky's attempted cross from the left floats over Jose Reina and nestles in the far corner. The game is turning into a nightmare for Liverpool's Spanish keeper.
63 mins: And three minutes later, the disiplinary scores are level as Jamie Carragher is booked for bringing down Ashton.
60 mins: An hour gone and West Ham's Dean Ashton receives the first booking of the final for a foul on Steve Finnan.
54 mins: Liverpool 2-2 West Ham
Surprise surprise, Liverpool's unstoppable captain Steven Gerrard completes his side's recovery from 2-0 down with a stunning volley into the top corner after Peter Crouch's knockdown.
50 mins: Djibril Cisse has changed footwear. The fashion-conscious Frenchman played the first-half in one white boot and one red but is now sporting bright yellow ones.
48 mins: It's an awful start to the second half for Liverpool. Harry Kewell has improbably injured himself running out for the second half and is replaced by Fernando Morientes.
46 mins: West Ham go agonisingly close to making it 3-1. Matthew Etherington races down the right and finds Marlon Harewood, whose shot is well stopped by Jose Reina. Reina then blocks Yossi Benayoun's follow-up.
46 mins: Liverpool get the second half underway as their fans urge them on with a rendition of 'You'll never walk alone'. Both sides are unchanged.
"We couldn't believe it when we went 2-0 up. Hopefully we can get another one and kill the game off. We know they'll come out with an onslaught so it's a question of riding that out."
Suspended West Ham midfielder Hayden Mullins
"It's impossible that Liverpool will be as bad in the second half as they were for 20 minutes of that first half"
BBC Sport pundit Alan Hansen
"Considering he might not be 100% fit, Dean Ashton has been the star of the show so far"
BBC Sport pundit Alan Shearer
HALF-TIME: As the players troop in at the interval, there's no doubt which set of fans is the happiest as the Hammers' fans drown out their Liverpool rivals.
44 mins: It could be famous last words but the action seems to have settled down again as half-time approaches.
40 mins: Liverpool switch systems. Harry Kewell is now playing just off Peter Crouch, with Djibril Cisse on the left.
37 mins: Dean Ashton is inches away from making it 3-1, cutting through the Liverpool defence and firing it across Jose Reina and just wide.
32 mins: GOAL Liverpool 1-2 West Ham
Steven Gerrard does his Captain Marvel act again, lifting the ball over Lionel Scaloni to where Djibril Cisse is waiting to slam home. This is a remarkable game so far - and there are only 32 minutes gone!
31 mins: The West Ham fans are celebrating again as Peter Crouch has the ball in the net from Steven Gerrard's free-kick - and the linesman flags for offside.
28 mins: GOAL Liverpool 0-2 West Ham
Liverpool are left reeling as the underdogs double their lead. Jose Reina fumbles Matthew Etherington's shot and Dean Ashton pokes the ball home.
23 mins: The bubbles are flying in Cardiff. Liverpool boss Rafa Benitez looks stunned on the bench. The Reds' famously resolute defence has been breached by an error from one of their own.
21 mins: GOAL Liverpool 0-1 West Ham
Xabi Alonso gives the ball away in midfield and Dean Ashton finds Lionel Scaloni with an inch-perfect through-ball. His cross is diverted past Jose Reina by Liverpool defender Jamie Carragher.
19 mins: With nearly 20 minutes gone, there is little to choose between the two sides. Liverpool, however, are perhaps looking a little less anxious than the opposition.
13 mins: Carl Fletcher gives away a free-kick 30 yards out with a foul on Steven Gerrard. John Arne Riise's effort does not lack power but is directed straight at the wall.
11 mins: Marlon Harewood powers through on goal but his shot is deflected for a West Ham corner.
10 mins: Liverpool skipper Steven Gerrard gives the ball away for the second time in the opening 10 minutes.
6 mins: Peter Crouch is clearly feeling confident. The England striker attempts an overhead kick from outside the area. It bounces once before trickling out midway between the goal and the corner flag.
5 mins: Yossi Benayoun escapes down the right for West Ham, but Sami Hyypia cuts out his cross with Dean Ashton and Marlon Harewood lurking.
1 min: The nerves get to Paul Konchesky immediately as he brings down Steven Gerrard with a horribly mistimed challenge, but Liverpool's free-kick comes to nothing.
1500 BST: West Ham kick off the 125th FA Cup final.
Build-up (all times BST):
1454: The players and coaching staff of Liverpool and West Ham are greeted by Prince William, on his first official outing as Football Association president. The prince towers over both Liverpool captain Steven Gerrard and West Ham counterpart Nigel Reo-Coker.
1451: A huge roar goes up in the Millennium Stadium as the teams emerge from the tunnel. Michael Ball sings the National Anthem.
1446: Lesley Garratt leads the fans in a rousing rendition of 'Abide with me'.
1443: With just under 15 minutes until kick-off, BBC analysts Alan Shearer and Alan Hansen tip Liverpool to win. Londoner Ian Wright plumps for West Ham "all the way".
"At last I've spotted some real Eastenders. Minty and Gary Hobbs are on their way to the stadium. No sign of the Mitchells though"
BBC Sport's Jonathan Stevenson in Cardiff
1426: Legendary Aussie spin bowler Shane Warne is on the pitch to present the match ball for the final.
1424: West Ham manager Alan Pardew tells BBC Five Live he does not expect Dean Ashton and Matthew Etherington to last 90 minutes, but adds that they will hopefully come off once the Hammers are leading.
1421: England 1966 hero Sir Geoff Hurst tells BBC Five Live he never doubted current West Ham boss Alan Pardew, who was under intense pressure as the Hammers struggled in the Championship last season.
1416: Skipper Nigel Reo-Coker is all smiles as West Ham warm up in Cardiff. The midfielder is hoping to celebrate his 22nd birthday on Monday with the FA Cup trophy in his hands.
1355: Both teams receive a boost with just over an hour to go before kick-off. Dean Ashton and Matthew Etherington are fit to start for West Ham while Xabi Alonso has shaken off an ankle injury to take his place for Liverpool. Djibril Cisse partners Peter Crouch up front, with Fernando Morientes on the bench.
FA Cup final teams
1353: Speaking on BBC Five Live, Sir Trevor Brooking says "not one week" goes by without someone reminding him of his winning goal for West Ham in the 1980 final. That may not be the case after today - if the Hammers upset Liverpool.
1338: Liverpool are out on the pitch greeting the fans who have arrived at the stadium early. Meanwhile, in the BBC Sport studio, veteran comic Jimmy Tarbuck tells Gary Lineker: "Liverpool would win if the final were on paper, but it's on grass."
1322: As the Hammers go for their walkabout on the pitch, Liverpool arrive at the stadium. They've gone for a more traditional look: white shirts and red ties.
1313: West Ham arrive at the Millennium Stadium. Alan Pardew and his players have taken the brave decision to wear pink shirts and ties.