From 1980 to 1991, 236 patients with renal cell carcinoma were treated in our department. We studied the characteristics and the prognostic significance of 74 patients with incidental renal cancer in comparison with those with symptomatic tumors. The mean age of the patients was 59.8 years and the sex ratio 2 males/1 female. The incidence of incidental tumors increased from 14% in 1980 to 48% in 1991. Incidental tumors were discovered mainly during examination for cardiovascular diseases (26%), hepatobiliary diseases (22%) and general health examination (23%). Local tumoral stage and histologic grade were significantly lower for the incidental tumors than for symptomatic ones (p = 0.002 and p = 0.001). In the same way, the rates of the patients with metastases or nodal involvement were lower for those with incidental tumors than for those with symptomatic tumors (p = 0.008 and p = 0.001). The mean tumoral size was 5.7 +/- 3 cm for incidental tumors and 7.6 +/- 3.5 cm for symptomatic tumors (p = 0.0001). The survival was significantly different according to the circumstances of detection of the tumors (p < 0.001); the 5- and 10-year actuarial survival rates was 85% for the patients with incidental tumors and respectively 61 and 44% for the patients with symptomatic tumors. The multivariate analysis by Cox proportional hazard model showed three important and independent prognostic factors: the presence of metastases (relative risk (RR): 6.7), nodal involvement (RR: 4.6) and symptomatic tumors (RR: 1.7). The patients with incidental tumors had a better prognosis than those with symptomatic tumors because of lower tumoral size and local stage. The early diagnosis of renal cell carcinoma improved the prognosis of the patients.