The 23-year-old, who had a year left to run on his current deal, will remain at Loftus Road until 2009.
Cook told the club's website: "The club are moving forward. There's no way I would want to miss the success I think this club will have next season.
"As a QPR fan there is no better feeling than being able to play for the club you love, but you also have to use your common sense," he added.