198 (3.8% comprising 4.7% of the males and 2.9% of the females) out of 5220 surgical patients developed total urinary retention postoperatively. The frequency of this condition increased with age and was highest after thoracotomies and endoprosthetic surgery of the hip joints. Voiding history was abnormal in 80% of the patients affected. Subclinical obstructive bladder dysfunction, over-distension of the bladder during the operation and in the recovery room after the operation, sympathomimetic and anticholinergic medication during or after anaesthesia, and an inability to stand or sit after surgery were common causes of retention. Premedication, type of anaesthesia, nature of the liquids given and postoperative analgetics seemed not to affect the incidence of retention. Postoperative urinary retention is an underestimated and mostly avoidable complication. Every patient should be asked for a urinary history before an elective operation. Infravesical obstruction should be relieved before any other elective surgical procedures are undertaken. In cases of emergency surgery prophylactic catheterization to prevent postoperative retention is recommended for patients with obstructive symptoms.