A case of primary signet ring cell carcinoma of the urinary bladder is reported. A 52-year-old man was admitted with the complaint of gross hematuria. Cystoscopy showed non-papillary tumor on the right lateral wall. Abdominal CT, Ga scintigraphy, upper gastrointestinal series and barium enema, revealed no signs of a tumor other than the bladder carcinoma. The routine hematologic and chemistry profiles showed no abnormalities except for the serum level of carcinoembryonic antigen elevated to 210 ng/ml. Total cystectomy and right nephroureterectomy with left cutaneous ureterostomy was performed and the surgical specimen showed adenocarcinoma of the bladder. The patient died 5 months after the operation, and autopsy was performed. No tumors were found on the mucosa of the whole digestive tracts or pancreas. This case might be of primary adenocarcinoma originated from the bladder. The literature on the differential diagnosis of the cases reported as bladder adenocarcinoma are reviewed briefly.