PURPOSE: To evaluate the usefulness of color/power Doppler ultrasonography (US) in differentiation between small renal cell carcinomas (RCCs) and angiomyolipomas based on the vascular distribution on color/power Doppler ultrasonography. MATERIALS AND METHODS: Retrospective analysis of color/power Doppler US findings of twenty patients with small renal tumors less than 3 cm in size and twenty patients with angiomyolipoma was done. The vascular distribution on color/power Doppler US was classified into: pattern 1=no flow signal, pattern 2=intratumoral focal flow signal, pattern 3=penetrating flow signal and pattern 4=peripheral flow signal. Statistical analysis was done using Fisher's Exact Test, at 99% confidence level. RESULTS: Among 20 patients with RCCs, 13 patients had pattern 3 or pattern 4 whereas among 20 patients with angiomyolipoma, 17 patients, pattern 1 or 2. There was a statistically significant difference in the vascular distribution between two groups (p<0.01). CONCLUSION: Color/power Doppler ultrasonography showed a distinct difference in vascular distributions for renal cell carcinomas and angiomyolipomas with a statistical significance. Therefore, color/power Doppler US is useful in differentiating renal cell carcinomas from angiomyolipomas.