A detailed histological analysis of 21 prostatectomy specimens for stage A1 disease was performed. Three cases (14 per cent) demonstrated no tumor, although all had foci of severe dysplasia. Of the prostates 18 (86 per cent) contained residual tumor: 13 (62 per cent) had minimal residual tumor and 5 (24 per cent) had substantial tumor. The residual carcinoma in the prostates with minimal tumor was predominantly in the apex of the gland or peripherally adjacent to the capsule such that complete removal by repeat transurethral resection would have been unlikely. Of the 5 specimens with substantial tumor, although some would have been upstaged by repeat transurethral resection, others would have remained stage A1 because of the peripheral location of the residual tumor. Within the definition of stage A1, using either the percentage of tumor involvement, weight of tumor or number of tumor foci in the transurethral resection specimen, one could not predict whether the prostatectomy specimen would have no, minimal or substantial residual tumor. Postoperatively, all patients are continent and 93 per cent are potent. Because some men with stage A1 carcinoma of the prostate will have substantial residual tumor not necessarily detected by repeat transurethral resection and the majority will have minimal residual tumor, which also appears to have an increased long-term risk of progression, radical prostatectomy should remain an option in the management of relatively young men with stage A1 disease.