Transvaginal ultrasonography and color flow imaging, performed to investigate whether there is any diagnostic advantage, were assessed over a 3 year period in 217 patients with adnexal masses prior to explorative laparotomy. Gray scale sonography and color Doppler flow were performed 1 day prior to surgery. Benign tumors were found in 165 patients and flow was detectable in 82 (49.7%); 14 patients had tumors of low malignant potential, 12 (85.7%) of whom showed detectable flow, and 38 had malignant tumors, in 25 (65.8%) of whom flow was detectable. Blood flow velocity was evaluated by the calculation of the resistance index prior to surgery. Mean resistive index was 0.39 +/- 0.05 for malignant tumors, compared with 0.49 +/- 0.06 and 0.55 +/- 0.07 for the low malignant potential and benign tumors, respectively. These differences were statistically significant (P < 0.01). When a resistive index of 0.47 was considered the cut-off value, the sensitivity was 88% and the specificity was calculated to be 85% (using color Doppler flow as the only diagnostic method). With our large cohort of patients, we demonstration the contribution of color Doppler flow examination in differentiating benign from malignant ovarian tumors prior to surgery.