A study of 28 patients with surgically proved testicular tumors was performed to determine the appearance at color Doppler ultrasound (US) scanning. There was a general correlation of tumor size and vascularity. Twenty of 21 (95%) tumors larger than 1.6 cm were hypervascular. Six of seven (86%) tumors smaller than 1.6 cm were hypovascular. One small, 1.1-cm-diameter seminoma was hypervascular, and one 2.8-cm-diameter seminoma was hypovascular. The histologic findings of the tumor did not correlate with the vascularity of the lesion as seen at color Doppler US. Resistive indexes ranged from .476 to 1.0 (mean, 0.70). Peak systolic velocities ranged from 8.4 cm/sec to 64.9 cm/sec (mean, 9.8 cm/sec). Venous flow was detected in eight tumors. The gray-scale findings, as well as history and physical examination findings, correctly suggested a neoplasm in all cases. The findings at color Doppler US were prospectively interpreted as indicative of neoplasm in 27 cases and as indicative of inflammation in one case. The authors conclude that color Doppler US scanning has only a limited role in the evaluation of testicular tumors.