The incidence of kidney cancer has been rising over the last two decades, especially in cases where the disease is localized. Although rates of renal surgery parallel this trend, mortality rates have continued to rise. To investigate the basis of this "treatment disconnect" (i.e., increased rates of treatment accompanied by increased mortality rates), we analyzed patient data from nine registries of the National Cancer Institute's Surveillance, Epidemiology, and End Results Program. We assembled a cohort of 34,503 kidney cancer patients and derived incidence, treatment, and mortality trends for kidney cancer, overall and as a function of tumor size. From 1983 to 2002, the overall age-adjusted incidence rate for kidney cancer rose from 7.1 to 10.8 cases per 100,000 US population; tumors < or = 4 cm in size accounted for most of the increase. Adjusted rates of renal surgery increased concurrently, most notably for tumors < or = 4 cm (0.9-3.6 surgeries per 100,000 US population). However, among kidney cancer patients, all-cause mortality per 100,000 US population increased from 1.5 deaths in 1983 to 6.5 deaths in 2002, with the greatest absolute increase noted for patients with lesions > 7 cm. Our results demonstrate that the rising incidence of kidney cancer is largely attributable to an increase in small renal masses that are presumably curable. The fact that increased detection and treatment of small tumors is not reducing mortality argues for a reassessment of the current treatment paradigm.