Emergency sonographic examination of the pelvis was performed in 41 girls (mean age, 13 years old) with clinical suspicion of ovarian torsion. Sonographic features consistent with diffuse swelling of the ovarian parenchyma and follicular enlargement in the cortical zone were detected in eight patients and were considered highly suggestive for torsion of the ovary. Surgery revealed ovarian torsion in seven of these cases and hemorrhagic ovarian cyst in one case. A cystic or complex ovarian mass was detected by sonography in five additional cases, and ovarian torsion was included in the differential diagnosis. Surgery revealed ovarian torsion in four of these cases and hemorrhagic ovarian cyst in one. A 100% sonographic sensitivity for space-occupying disease of the ovary was obtained with a positive predictive value of 88% for the diagnosis of ovarian torsion. The specificity of the method was 93%. Sonography appears to be an excellent method to evaluate patients with suspected torsion of the ovary.