PURPOSE: To present a diagnostic sign on MRI and US in patients with ovarian torsion. MATERIALS AND METHODS: We present characteristic imaging findings in eight patients with surgically-proven ovarian torsion. MRI was performed in four patients, CT in six and US in all patients; the procedures including eight transabdominal US(TAS) and three transvaginal US(TVS). In each study, imaging findings were analyzed for the appearance of twisted pedicle and the presence of a "whirling sign". RESULTS: The pedicle which indicates ovarian torsion was detected on MRI in all 4 patients, on TAS in 4/7, on TVS in 3/3, and on CT in 4/6. A specific "whirling sign" was detected on MRI in 2/4 patients, on TAS in 2/4, and on TVS in all three. On CT a "whirling sign" was not detected. CONCLUSION: The "whirling sign" on both MRI & US is a characteristic finding of ovarian torsion; in a patient with adnexal mass and complaining of lower abdominal pain, the presence of this sign is very useful for the diagnosis of ovarian torsion.