Purpose : To compare MRI appearance between plicae syndrome and normal plicae. Materials & Methods : MR imagesof 60 cases of arthroscopically-confirmed plicae syndrome and 18 of arthroscopically-proven normal plicae wereretrospectively analyzed. Sagittal T2-weighted MR images in all cases and MPGR(200) in 37 cases of plicae syndromewere obtained. Statistical analysis was performed using the chi-square test. Results : On the basis of operatingresults, we observed 55 medial plicae, eight combined medial and suprapatellar plicae, four suprapatellar plicae,and one lateral plica. T2-weighted sagittal MR scans of the 60 cases demonstrated 37 medial plicae, 8suprapatellar and one lateral plica. Joint effusion was found in 26 cases of 55 medial plicae. In T2-weightedsagittal MR scans, the identification of medial plicae was superior in the presence of joint effusion than itsabsence(plicae syndrome, p < 0.001 ; normal plicae group, p < 0.05). Medial plicae were well demonstrated onMPGR(200) axial images; on T2-weighted sagittal MR scans, they could be more frequently identified in the plicaesyndrome group than in the normal control group(p < 0.001). Plicae syndrome-associated pathology includeddegenerative change of the articular cartilage of the medial femoral condyle in eight cases(14.5%), discoidmeniscus in nine(16.4%), lateral meniscus tear in 12(21.8%), medial meniscus tear in 21(38.1%), anterior cruciateligament tear in three(5.5%), medial collateral ligament tear and osteochondritis dissecans in one case.Conclusion : The present study revealed that synovial plicae were well demonstrated in T2-weighted sagittalimages, particularly on the presence of joint effusion. Medial plicae could be more frequently identified in theplicae syndrome group than in the normal control group, especially on T2-weighted sagittal MR scans.