PURPOSE: To evaluate the usefulness of ultrasonography (US) and color Doppler sonography (CDS) in the diagnosis of adnexal torsion in pregnancy. MATERIALS and METHODS: US and CDS findings of 31 patients with surgically proven adnexal torsion during pregnancy were retrospectively reviewed. On US, the presence of a twisted vascular pedicle (TVP), ovary, or adnexal mass were evaluated while the presence of blood flow within the TVP and ovary or adnexal mass were evaluted on CDS. Adnexal torsion was diagnosed by the detection of TVP and absent flow to the ovary, and the diagnostic accuracy of US was assessed. RESULTS: TVP was detectable on US in 25 of 31 cases (80.7%) with adnexal torsion during pregnancy. In four cases, torsion of the ovary was seen as the multiple peripherally located follicles in the enlarged ovary, and in one case, torsion of the hyperstimulated ovary appeared as multiple cysts measuring between 2 to 7 cm in diameter combined with swollen parenchyma. Ovarian mass was detected on the same side of the torsion in 27 cases, the diameter ranging from 3.5 to 22 cm (mean = 8.4 cm); 15 of them were mostly cystic while nine masses with the mixture of cystic and solid portions and two masses consisted of solid portion were also observed on US. The blood flow was present in the twisted vessels on CDS in 13 of 25 cases with TVP, and flow within the ovary or an adnexal mass was seen in 12 cases. The remaining 12 cases showed no flow within TVP and the ovary. In six cases with no visible TVP, the blood flow of the ovary was present in five cases and absent in one case. Torsion was confidently diagnosed in 25 cases with the visible TVP and in one case with absent ovarian flow on US and CDS, showing the diagnostic accuracy of 83.9%. CONCLUSION: US and CDS can be useful diagnostic modalities in the diagnosis of adnexal torsion in pregnancy.