We report the results of a prospective study about the detection of tumoral neovascularization, the renal vein involvement and the characterization of renal tumors by color and pulsed doppler. Twenty-six renal tumors including 19 renal carcinomas and 7 benign tumors (2 angiomyolipomas, 2 oncocytomas, 2 complex cysts and one adenoma) were prospectively explored. Benign cysts were excluded from the study. The results were correlated to pathologic (24/26) and angiographic datas (24/26). Doppler ultrasonography seems to be an accurate method for the detection of a neovascularization (19 true-positives/19 vascularised tumors, no false-positive) but pulsed doppler (no false-negative) is more sensitive than color doppler imaging (3 false-negatives), the results of color doppler were improved by using a new software for the color detection of very low flow. Spectral analysis found 3 different types of doppler curves inside the masses, but all of them were observed in benign and malignant tumors. We did not find any correlation between the size of the tumor and the peak systolic velocity. The specificity of Doppler regarding the renal vein and inferior vena cava involvement seems to be good (no false-positive). But as, in our series, we do not have any case of main renal vein involvement, the sensitivity of this technique cannot be assessed.