Femoral anteversion (AV) was determined by ultrasound in 40 adolescent and adult patients with rotational disorders of the femur, and the results were compared with AV measurements by biplanar roentgenography. With the patients supine, their knees flexed 90 degrees, and their lower legs strapped in the vertical position, one scan only of the proximal femur was needed to measure the anteversion by ultrasound. The transducer was tilted until the desired measuring line appeared horizontal on the monitor screen. The angle of tilt of the transducer, which represented the AV angle, was measured with an attached clinometer. The correlation between ultrasound and roentgenographic AV angles was high, indicating that reliable results were obtained by ultrasound. The preferred reference line was the head-trochanter tangent, which is recommended for clinical use. Consistently greater AV values were measured by ultrasound than by roentgenography. Thus, 10 degrees should be subtracted from the ultrasound values in order to obtain the real AV angles. One of the benefits of ultrasound is the elimination of radiation hazards to the patients. Ultrasound is recommended as a screening technique for patients with rotational disorders of the femur.