Abstract Purpose We determined the risk of local recurrence in 64 Japanese patients a median of 69 years old with renal cell carcinoma who were possible candidates for nephron sparing surgery and who underwent radical nephrectomy. Materials and Methods A total of 64 kidneys in which tumors 50 mm. or less were resected were prospectively examined pathologically in 3 mm. sections. The incidence of satellite tumors and the relationship between the pathological findings of the primary and satellite tumors were evaluated. Results Satellite tumors were identified in 10 of the 64 kidneys (15.6%), a rate similar to that reported in the United States. The correlation of histological findings between primary and satellite tumors was 70% for tumor grade. Satellite tumor grade was less than that of the primary lesion in 3 cases. In 60% of the specimens with multifocal renal cancer satellite tumors were within 10 mm. of the margin of the primary tumor. At this distance, if partial nephrectomy had been performed, the satellite lesions would have been missed in 4 of these 10 patients (40%). Of the 10 kidneys with satellite renal tumors 8 (80%) had vascular invasion of the primary tumor. Multiple logistic regression analysis demonstrated that vascular invasion was a significant predictor of multifocality of renal cell carcinoma. Conclusions Our results suggest that vascular invasion is a risk factor for multifocality in Japanese patients with renal cell carcinoma. Therefore, careful and long-term followup is necessary in patients with renal cell carcinoma who have undergone nephron sparing surgery, especially those with vascular invasion of the primary tumor.