We examined the association between prostatic cancer incidence rates and the rates of transurethral prostatectomy to explore reasons for the nationally reported dramatic increases in incidence rates of prostatic cancer from 1973 through 1986. There was a strong correlation between both incidence of all stages of prostatic cancer combined and of localized disease and the increasing use of transurethral resection, a common surgical procedure usually performed to relieve urinary obstruction due to benign enlargement of the prostate. Our analyses suggest that increased detection of existing tumors via transurethral resection was the primary reason for the observed increase in incidence rates of prostatic cancer. However, analyses of mortality trends, particularly among nonwhites, and laboratory studies of the histologic nature of clinically asymptomatic tumors suggest that part of the increase may reflect changes in the real risk of prostatic cancer.