A 63-year-old man presented with haematuria and suprapubic pain. After transurethral resection of the prostate a tumour was seen in the bladder dome at cystoscopy. Biopsy revealed an adenocarcinoma. Based on intraoperative and histological examination of the partial cystectomy specimen, the tumour was judged to be an urachus carcinoma. Four years after diagnosis the patient has no evidence of tumour. While partial cystectomy is the most frequent treatment, a radical total cystectomy is advocated in poorly differentiated tumours.