Ovarian torsion is caused by rotation of the ovary or adnexa with the vascular pedicle on its axis resulting in arterial and venous obstruction. Here we report a case of a pregnant woman presented to the emergency department in early second trimester with acute abdomen. History revealed the presence of an ovarian mass detected by ultrasonography 6 months before pregnancy. Sonographic examination showed right adnexal mass with abnormal Doppler velocimetry and thus immediate laparotomy was decided. Right salpingo-oophorectomy was performed and post-operative course of the patient was uneventful. According to this case, adnexal torsion should not be eliminated from differential diagnosis when it comes to pregnant women with acute abdomen.