Kromkamp started out as a midfielder with Go Ahead Eagles in the 1998/99 season in the Dutch second division. He was sold to first division AZ Alkmaar before the 2000/01 season where he was transformed into a right-back. His exploits in the UEFA Cup in the 2004/05 season when AZ reached the semi-finals caught the attention of Valencia, Porto, Arsenal and Villareal. After discussions with Porto fell through Villareal was quick to snap him up. However, he had trouble adjusting to Spain and after only 11 games and five months into his five-year-contract he went to Liverpool in a straight swap with Josemi. Kromkamp couldn't dislodge Steve Finnan from his position but he did finish his debut season in a blaze of glory as a sixty-seventh minute substitute for Xabi Alonso in the 2006 FA Cup final which went to penalties. Seven months after his arrival homesick Kromkamp returned to Netherlands at the last day of the transfer window without having made a real impression at Liverpool. He won the Eredivise two years in a row at PSV from 2007-2008. After missing 18 months due to injuries he rejoined his first club, second division Go Ahead Eagles, in February 2011.
Kromkamp made only fourteen first-team appearances for Go Ahead Eagles Deventer in 2012/13 having made double that number in 2011/12. He announced his retirement as a player towards the end of June 2013 at the age of thirty-two because of chronic knee problems, but remained at the club as a coach of the under 16's side and by 2018 had progressed to be in charge of their under 19's.
|2||West Ham United|
|1||07.01.2006||Luton Town||Kenilworth Road||FA Cup|
"As both players have discovered, it is difficult to play in an other country. Josemi has tried to learn English and he's improved a lot but for him and his family it has been hard. Kromkamp has suffered the same in Spain. He speaks English but at Villarreal almost everyone speaks Spanish so it was not an ideal situation for him."
Rafa on Jan Kromkamp who joined Liverpool in January 2006
|Club||Season||Club rank||League apps||League goals||Total apps||Total goals|
|Go Ahead Eagles||1998-1999||Netherlands 2||28||1||28||1|
|Go Ahead Eagles||1999-2000||Netherlands 2||33||4||33||4|
|AZ Alkmaar||2000-2001||Netherlands 1||25||2||25||2|
|AZ Alkmaar||2001-2002||Netherlands 1||22||1||22||1|
|AZ Alkmaar||2002-2003||Netherlands 1||25||2||25||2|
|AZ Alkmaar||2003-2004||Netherlands 1||34||0||46||0|
|AZ Alkmaar||2004-2005||Netherlands 1||27||1||39||1|
|PSV Eindhoven||2006-2007||Netherlands 1||28||0||36||1|
|PSV Eindhoven||2007-2008||Netherlands 1||26||1||35||1|
|PSV Eindhoven||2008-2009||Netherlands 1||12||0||13||0|
|PSV Eindhoven||2009-2010||Netherlands 1||2||0||4||0|
|Go Ahead Eagles||2011-2012||Netherlands 2||26||0||29||0|
|Go Ahead Eagles||2012-2013||Netherlands 2||8||0||14||0|