PURPOSE: To evaluate the MR findings of transient synovitis of the hip in children. MATERIALS AND METHODS: Between 1993 and 1997, MR imaging was performed in 30 children(male:female=22:8) in whom transient synovitis had been clinically diagnosed. In 20 of these 30 patients, Gd-en-hanced study was also performed. The signal intensity of bone marrow of the femur, the synovial enhancement pattern and the amount of hip joint effusion in affected hips were evaluated; the last-mentioned was determined using the volume measurement method. RESULTS: In 29 patients(97 %), no abnormal signal intensity was seen in bone marrow of the femur in affected hips. Gd-enhanced MR imaging revealed synovial enhancement of affected hip joints, as follows: minimal en-hancement in eight patients(40 %), moderate enhancement in eight(40 %), and strong enhancement in four( 20%). No abnormal enhancement was demonstrated in bone marrow of the femur or adjacent soft tissue. The mean amount of joint effusion of affected hips was 2.7 +/- 1.7(range, 0.2 -18.9)ml; statistically, this was much greater than that of contralateral hip (p<0.01). CONCLUSION: The MR findings of transient synovitis of the hip in children were normal bone marrow signal intensity of the femoral head, moderate or strong synovial enhancement, and asymmetric hip joint effusion.