To draw attention to the disregarded malignancy risk after ileocystoplasty, we present two cases of adenocarcinoma. The first case was metastatic at initial diagnosis. Despite chemotherapy, the condition progressed and the patient died at the 9th month. The second patient has received cystectomy followed by chemotherapy and radiotherapy. Although the second patient was an immunosuppressed renal transplant, she was disease-free at the 27th month. As the malignancy risk after bladder augmentation is a proven fact, until the discovery of a proper diagnostic method, we recommend doing routine annual cystoscopic biopsy starting after the 10th year of ileocystoplasty.