Background and objective Post-operative urine retention is a frequent and serious complication. The aims of this study were to evaluate the prevalence of post-operative urinary retention in a general surgical population and to identify the perioperative risk factors for developing this condition. Methods Data were obtained from 334 consecutive adult surgical patients, operated without a urethral catheter placed from 1 June to 13 July 2006. A bladder scan was performed within 30 min of arrival to the recovery ward, in case of bladder symptoms, and before referral to the surgical ward. Postoperative urinary retention was defined as a bladder volume above 600 ml and insufficient voiding within 30 min. Results Mean age (SD) was 58.6 years (+/- 16.6). One hundred and eighteen men (35.3%) and 216 women (64.7%) were included. The prevalence of post-operative urinary retention was 4.8%. Significant independent risk factors were diabetes mellitus (odds ratio, 5.9; 95% confidence interval, 1.760-19.882) and administration of atropine intraoperatively (odds ratio, 5.9; 95% confidence interval, 1.005-34.680). Conclusion The risk of developing post-operative urinary retention is approximately 5% in the present general surgical population studied, and co-existing diabetes mellitus and administration of atropine intraoperatively are pre-disposing factors. Eur J Anaesthesiol 2011;28:190-194 Published online 4 January 2011