A non-invasive ultrasound imaging technique (BladderScan) was used prospectively in an attempt to reduce the need for catheterization of the urinary bladder and the incidence of urinary tract infections after orthopaedic surgery. Over a 4-month period, in which 1920 patients were included, catheterization was performed if there was no spontaneous diuresis by 8 h after surgery. A total of 31% of these patients were catheterized, and 18 patients developed urinary tract infections. In a subsequent 4-month period, there were 2196 patients, catheterization was performed only if the bladder volume was more than 800 mL 8 h after surgery. The rate of catheterization decreased to 16%, and five patients developed urinary tract infections. In our patients, measuring bladder volume reduced the need for a urinary catheter and the likelihood of urinary infection.