PURPOSE: To compare MRI appearance between plicae syndrome and normal plicae. MATERIALS AND METHODS: MR images of 60 cases of arthroscopically-confirmed plicae syndrome and 18 of arthroscopically-proven normal plicae were retrospectively analyzed. Sagittal T2-weighted MR images in all cases and MPGR(200) in 37 cases of plicae syndrome were 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, 8 suprapatellar and one lateral plica. Joint effusion was found in 26 cases of 55 medial plicae. In T2-weighted sagittal MR scans, the identification of medial plicae was superior in the presence of joint effusion than its absence(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 plicae syndrome group than in the normal control group(p < 0.001). Plicae syndrome-associated pathology included degenerative 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 cruciate ligament 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 sagittal images, particularly on the presence of joint effusion. Medial plicae could be more frequently identified in the plicae syndrome group than in the normal control group, especially on T2-weighted sagittal MR scans.