OBJECTIVES: To conduct a population-based study to evaluate the effect of incidental detection of renal cell carcinoma (RCC) on survival. Incidental detection of RCC has increased significantly in recent years because of widespread use of abdominal imaging. The patients with incidentally diagnosed RCC have better survival; however, because of possible "lead time" bias and stage migration, the real implications of incidental detection on survival have been a matter of debate. METHODS: All living patients diagnosed with RCC in Iceland between 1971 and 2000 were included (n = 701). The histologic findings were verified, the stage (extent) of the disease was determined, and the incidence, mortality, and survival were evaluated. RESULTS: The strongest predictors of mortality were stage and nuclear grade. After correcting for these factors in the multivariate analysis, incidental diagnosis, histologic subtype, and gender lost their significance as independent prognostic factors of death. However, the incidentally diagnosed tumors were 2.3 cm smaller on average and at a lower stage and grade than symptomatic tumors, with significantly better patient survival than those with symptomatic tumors on univariate analysis (76% versus 44% 5-year disease-specific survival). An increased incidence of RCC was only seen in men, but incidental detection increased threefold during the study period in both sexes, with significant improvement in survival for the whole group as a result. CONCLUSIONS: The increased frequency of incidental detection has improved the survival of patients with RCC in Iceland. Incidental detection was not an independent prognostic factor of death, indicating that these tumors are of a similar biologic nature as symptomatic RCCs, only diagnosed earlier.