Since 1981 we have studied 34 patients with renal cell carcinomas smaller than 3 cm, diagnosed by US and IVP, to evaluate the diagnostic viability of these 2 procedures. Their respective results were compared to pathologic findings and tumor grading. No correlation was found between the type of sonographic patterns and the pathologic findings. On the contrary the correlation between the acoustic pattern and the grading, performed on small tumors and on a control group of large tumors, showed that most tumors in the former group (70%) had lower grading than those in the latter. We conclude that the introduction of US has changed the approach to the diagnosis of renal tumors, allowing their early recognition and characterisation. It is thus hoped that the clinical course of such tumors will be improved.