Transient synovitis of the hip joint in children is a self-limited disease presenting as an excessive joint effusion and synovial thickening. To evaluate the effectiveness of ultrasonography in the diagnosis of transient synovitis of the hip joint, a total of 31 hip sonograms in 28 patients was analysed retrospectively. Effusion of the hip joint was obseryed in 28 hip joints (90%) and synovial thickening in 22 (71%). The higher was the clinical gradiong, the larger was the amount of joint effusion and the more severe was the thickness of the synovium. We believe that sonography is a simple, non-invasive and accurate method of diagnosis and follow-up in patients with transient synovitis of the hip joint.