Three cases of mucous adenocarcinoma arising from the urachus are presented. The first case of female noticed abdominal tumor when she was 51 years old. She visited our hospital three years later. She died 4 years after initial symptoms, in spite of external radiotherapy with occasional good response. Other two cases of a 58-year-old female and a 35-year-old male complained gross hematuria and they received partial cystectomy elsewhere under the diagnosis of primary bladder cancer. They died 8 years and 6 years 9 months after the onset respectively, because of local recurrence. Radical operation in early period may bring a fruitful result.