We reviewed 66 patients with stage A adenocarcinoma of the prostate who were treated at our 7 affiliated hospitals in Yokohama between 1984 and 1988. Of 1377 patients who underwent subcapsular prostatectomy (SCP) or transurethral resection of the prostate (TUR-P) for benign prostatic hyperplasia, 66 patients (4.8%) were diagnosed as an incidental carcinoma of the prostate. Of these patients, 36 and 30 were in stage A1 and A2, respectively. In the 66 patients, 59 (4.5%) were detected in 1315 TUR-P and 7 (11.3%) in 62 SCP. Elderly patients over 80 years of age had a higher risk of stage A2 disease. In histological grade, well, moderately and poorly differentiated adenocarcinoma were found in 48 patients (72.7%), 13 (19.7%) and 5 (7.6%), respectively. Among the patients with stage A prostate carcinoma the majority of the age-group less than 79 years old had well differentiated adenocarcinoma. In the age-group more than 80 years old, there were 6 (37.5%) moderately and 2 (12.5%) poorly differentiated tumors. In other words, the age-group more than 80 years old tended to have the moderately or poorly differentiated adenocarcinoma more frequently than those other decades. We expect an increase in the number of patients with stage A2 disease in the future with the expansion of the operative indication, especially in elderly patients.