A boy with myelomeningocele who had sigmoidocolocystoplasty and ureteric reimplantation when 2-years old and normal annual cystoscopies, developed hematuria and abdominal pain with liver dysfunction 14 years postoperatively. Computed tomography showed a tumor on the left side of the augmented bladder, a large lymph node, and large multiple probable metastases in the liver. Cystoscopy 3 months earlier had been normal, but when repeated showed a tumor originating from the augmented sigmoid colon. Biopsy showed undifferentiated sarcoma. Despite chemotherapy, he died 3 months later. The diagnosis at autopsy was undifferentiated sarcoma originating from the sigmoid colon. We report the first case of undifferentiated sarcoma developing 14 years after sigmoidocolocystoplasty for meningomyelocele, and also review the 55 cases of post-bladder augmentation malignancy in the literature.