Eleven cases of primary adenocarcinoma of the bladder are described herein. Eight had a glandular pattern, 1 was papillary and 2 were comprised of signet ring cells (one had areas of colloid carcinoma). One of the cases, originating from the urachus, also showed colloid areas and a glandular pattern. Forty-five percent of the cases were moderately differentiated and the remaining 55% were poorly differentiated. In all cases the tumor had areas of adenocarcinoma in more than 2/3 of its extent. All but two cases revealed muscle layer infiltration at the time of diagnosis. Two patients were submitted to radical cystectomy, lymphadenectomy and Wallace II cutaneous ureteroileostomy, 1 patient underwent partial cystectomy and lymphadenectomy, and 6 were submitted to transurethral resection. Excision of the urachal tumor was by en bloc partial cystectomy. The 5-year survival of patients with infiltrating tumors, excluding the urachal tumor, was 33%, 67% died within the first year of follow-up. The only evaluable case of superficial adenocarcinoma is alive and tumor-free at 94 months. Primary adenocarcinoma of the bladder is an aggressive tumor. Although it may be superficial at the time of diagnosis, it soon develops into an infiltrating tumor if untreated. Treatment and survival depend on tumor stage. Superficial or minimally infiltrating tumors warrant treatment by deep transurethral resection up to the pericystium.(ABSTRACT TRUNCATED AT 250 WORDS)