BACKGROUND Urinary tract obstruction may damage the kidneys, but the interpretation of intravenous urograms is difficult after a total cystectomy for bladder cancer. There is a need for practical guidelines for image reading. MATERIAL AND METHODS Urograms were routinely taken to control 20 patients (18 men) who had been operated for bladder cancer with total cystectomy and urinary diversion between 1999 and 2004. All patients were examined one or several times at irregular time intervals after surgery. 18 patients were examined within six months after surgery, of whom six were also examined later. Two patients were only examined after six months. Two radiologists reviewed the postoperative urograms by first filling in a standardised form independently of each other and thereafter by filling in the form together according to consensus. The extent of dilatation of the collecting system (calyces, kidney pelvis and ureter) was graded as none, mild, moderate or severe for each side separately. RESULTS At the first follow-up within six months, six of 18 patients had developed moderate or severe and 10 mild dilatation of the collecting system. The left side was more often dilated (n=7) than the right one (n=1). Both sides were dilated for eight patients; to a moderate/severe degree for two and to a mild degree for six. Of the six patients who were also examined more than 6 months after surgery; one had moderate/severe persistent dilatation and showed signs of regression, three had mild dilatation (two of whom had remission) and two had no dilatation after six months. The patient with a persistently dilated collecting system lost one kidney on the left side despite insertion of a draining ureteral stent. There was a good interobserver agreement concerning the grade of dilatation. INTERPRETATION Mild dilatation of the collecting system is common after cystectomy and urinary diversion, especially on the left side, and will normalize within a few months in most patients. Persistent dilatation may signify a pathological condition, especially in combination with other radiological findings, such as delayed contrast excretion and obstructed passage in late images.