Early detection and management of prostatic cancer (PC) is an important public health problem in all industrialized countries, where the relative rate of the elderly population is rapidly increasing. We examined the epidemiology of PC in the province of Trieste, Italy and studied the relationship between prostatic intraepithelial neoplasia (PIN) and PC. The average annual incidence of PC was 99.3 per 100,000 (1,739 new prostatic cancer cases were histologically diagnosed at autopsy or in surgical specimens between 1980 and 1993). In patients over 85 years of age, the incidence rate was 1,209 per 100,000 compared with 64 per 100,000 in the 55-64 age group. Trends in PC incidence rates showed a significant increase among men under 64 years of age and those between 65-74 years. Survival analysis showed that 94% of the patients with well differentiated PC were alive at 5 years, compared with 80% and 40% of those with moderately differentiated and poorly differentiated cancer, respectively. We studied 130 whole autopsy prostates, 70 radical prostatectomies with carcinoma, 63 transurethral resections or adenomectomies without cancer from patients who later developed PC and 94 transurethral resections or adenomectomies from patients who did not develop PC. The 102 prostatic cases with cancer had a high rate of PIN, and the relative frequency of PIN 3 was high (almost 70%, versus almost 0% in benign prostates). In addition, the frequency of PIN was higher in benign prostates of patients who later developed PC (almost 50% of the cases) than in benign autopsy and surgical prostates. PIN was spatially associated with cancer in 75% of the cases. This study confirms the strong relationship between PIN and PC.