PURPOSE To assess the feasibility of Multislice spiral CT (MSCT) with volume rendering (VR) and maximum intensity projection (MIP) reconstructions in recognizing ureteropelvic junction obstruction (UPJO). MATERIALS AND METHODS Twenty-seven patients with UPJO underwent MSCT. To visualise the excretory system, 50 ml of uroangiografic contrast medium was administered by drip infusion via the cubital vein 180 minutes before the CT scan. MSCT was performed after the injection of 120 ml of contrast medium at a flow rate of 3.5 ml/sec. Dual-phase scanning was performed 25s and 55s after contrast medium administration. MIP and VR reconstructions were obtained on a dedicated workstation. RESULTS In 11/27 (41%) patients, UPJO was due to an anomalous ureteropelvic junction (UPJ). In 9/27 (33%), the stenosis was caused by anomalous vessels. In 3/27 (11%), stenosis was due to an anomalous UPJ position even though anomalous accessory vessels could be seen. In 4/27 (15%), anomalous vessels were also identified but the presence of a pyeloureteral stent did not allow us to establish whether these vessels were the cause of UPJO. CONCLUSIONS MSCT and MIP and VR reconstructions allow identification of the causes of congenital UPJO and provide useful information for appropriate treatment planning.