Neurofibromatosis of the urinary tract is estimated to account for 20 per cent of the visceral manifestations of the generalized disease. Among its urological forms involvement of the bladder is the most common. Clinically, neurofibromatosis resembles a tumour, therefore, its early histologic diagnosis is of utmost importance. In the present case a tumour involving the posterior bladder wall was found in a 6 years old boy subjected to examination because of a terminal haematuria. First the tumour was resected, later cystectomy with implantation of the distended ureter into the sigmoid was undertaken because of progression of the tumour. Postoperative hypokalaemia responded to the usual medication. Ureteral distension was reversed by the operation. Though neurofibromatosis (NF) is histologically a benign process, it tends to recur, is invasive, and impairs urinary functions. Therefore, it may endanger life and thus requires cystectomy with surgery for urinary diversion.