This report presents two cases of urachal signet-cell adenocarcinoma (USCA). Two men, aged 53 and 51 years, presented with haematuria. Cystoscopy showed tumours in the dome of the bladder and transurethral resection revealed signet ring cell carcinoma. They both underwent cystoprostatectomy but died of metastatic disease after 14 and 26 months. USCA is a very rare tumour with poor prognosis. Only 25 cases have been reported. The tumours have a specific gross and microscopic morphology but must be distinguished from metastases of signet ring cell originating from other sites. Immunohistochemistry is helpful for the determination of the primary site.