From 1989 to 1996, 61 patients, including 66 knees, aged 8 to 62, were diagnosed as mediopatellar plica syndrome of knee after arthroscopic examination. Twenty-one cases were misdiagnosed as medial meniscal lesions before arthroscopic examination. Fifty-nine patients (64 knees) underwent arthroscopic resection of the plicae and 2 patients underwent opened resection. Fifty-nine cases had an average follow-up of seven months. Fifty cases (54 knees) of them showed excellent and good results.