In this study the impedance to blood flow was examined by color Doppler sonography in fifty uterine masses before exploratory laparotomy. After measuring the Resistance Index (Rl) of the vessels in the neovascularization area in the mass, these values were compared with the pathology reports of each mass after surgery.It was seen that neovascularization area was present in all of the eight malignant cases. Rl values were less than 0.40 (the limit value) in all of the malignant cases. Neovascularization area was present in 38 (90%) of the 42 benign cases and all Rl values were greater than 0.40 in these cases (average 0.65).The sensitivity and specificity of preoperative Rl in detecting uterine malignancy were 100 %.Our results suggest that color Doppler sonography is a useful clinical tool in the preoperative evaluation of uterine masses.