In recent years, diagnostic imaging techniques, especially ultrasonography (US) and CT scanning, have been widely adopted in clinical practice, making early accurate diagnosis of renal tumors possible. A total of 452 cases of renal tumors have been admitted to the institute since 1951, of which 220 were seen from 1951 to 1979 and 232 in the past 9 years (1980-1988). The frequency of renal parenchymal tumors was obviously higher in the latter group, including asymptomatic renal carcinoma in 20.2% and hamartoma in 38.1%. All these were discovered on routine physical check-up by ultrasonography and/or CT scanning and would otherwise have gone undiagnosed on conventional urography. Ultrasonography and CT can also reveal the nature and the extent of the tumor. The idea that "a renal tumor should be considered malignant unless pathologically proven otherwise" is no longer valid. However, general manifestations of renal carcinoma, such as elevated erythrocyte sedimentation rate (ESR), hypertension, malaise, anemia, fever and hypercalcemia, still deserve proper attention. We suggest that ultrasonography of both kidneys should be mandatory in routine physical check-up, as far as the urinary system is concerned, in order to discover asymptomatic renal tumors.