We reviewed 74 patients with incidentally found renal cell carcinomas (20%) out of 366 patients treated in affiliated hospitals over the past 14 years. The annual rate of the incidentally found carcinomas has increased up to 40% of the total. CT scan and/or ultrasonotomography were used in the first diagnosis in 76% of these 74 patients. The prognosis for the incidental group was more favorable than that of the classical symptom group, since the former group consisted of patients with smaller-sized carcinomas which usually tend to be confined to the kidney.