Sixtysix patients were submitted to color doppler ultrasono graphy, with flowmetric analysis, in the preoperative work up of their thyroid nodules. Three different groups (and two subsets) were so identified, corresponding to the different pathological nodule types: hyperplasia, adenoma, and cancer. The data obtained were then compared to the final pathological results. The color doppler ultrasonography showed a diagnostic accu racy rate of 87.8%. An evaluation of the peak systolic velocity proved to be very useful in the differential diagnosis between adenomas and cancers. The color doppler ultrasonography represents a sound method for evaluating thyroid nodules.