The purpose of the study was to evaluate and compare opacification of the renal collecting system and ureters detected by computed tomographic urography (CTU) performed 20 min and 1 h after the ingestion of 1,000 ml of water. CTU was performed on 89 patients (55 men, 34 women; age 28-77 years) and 168 collecting systems and ureters were evaluated. A 16-detector-row scanner (Sensation 16, Siemens) was used; a two-phase protocol with a split bolus of contrast agent (total 120 ml) was applied. A combined nephrographic-excretory phase was obtained 100 s after the second injection. Three-dimensional reconstructions of the excretory phase were created and used to evaluate the degree of opacification of the collecting system and ureters. In 44 patients, water was administered 20 min before examination, and in 45 patients, 1 h before examination. CTU performed 1 h after water ingestion demonstrated complete opacification of calices in 87.5%, of renal pelvis in 97.5%, of upper ureter in 91.8% and of lower ureter in 87.5% of patients. CTU performed 20 min after water ingestion demonstrated complete opacification of calices in 79.5%, of renal pelvis in 85%, of upper ureter in 62.5% and of lower ureter in 54.5% of patients. Complete opacification of the proximal and distal ureter in the group with a 1-h delay was statistically higher (P<0.01). CTU performed on the distended bladder, 1 h after the oral ingestion of water, enables excellent opacification of collecting system, including distal ureters.