The utility of ultrasound in the primary examination of patients with Perthes disease was evaluated. Nineteen patients were examined with a longitudinal lateral and an anterior scan. Ultrasound was reliable in diagnosing Perthes disease when the surface of the ossified epiphysis was irregular and when fragmentation had occurred. There was good correspondence between ultrasound and radiography in assessment of femoral head coverage. Twelve patients had an increased anterior joint space, indicating accompanying synovitis. Femoral anteversion (AV) angles, measured by ultrasound, were significantly greater in the affected hips, but mean side difference (3 degrees) was moderate. Ultrasound provided useful information. Like conventional radiography, ultrasound showed the irregular structure of the bony epiphysis and the lateral coverage of the femoral head. In addition, the anterior coverage, an accompanying synovitis, and the degree of femoral AV were obtained. In the very early stage, the femoral head may look normal by ultrasound, but a persisting joint effusion arouses the suspicion of Perthes disease.