Postoperative retention of urine (PU) is a common complication which may occur after any surgical intervention. It may affect both sexes in all age groups and result in considerable morbidity. The frequency depends upon the type of operation and its duration but statements in the literature vary greatly on account of inaccurate and varying definitions and uncertain diagnostic criteria. Intervention in the true pelvis results in the highest frequencies of postoperative urinary retention. The method of anesthesia is of lesser significance. Spinal anesthesia and epidural morphine constitute, however, a particular risk for the development of postoperative retention of urine. The pathological physiology is complex and includes: 1) disturbance of the balance between the sympathetic/parasympathetic influence on bladder and urethral function, 2) drugs which inhibit the miction reflex, 3) anaesthesia and sedation which cloud the awareness of bladder filling, 4) rapid filling of the bladder with subsequent overdistension, 5) lesion of the nerve fibres to the lower urinary tract, 6) mechanical obstruction and 7) difficult positions and/or situations for miction. Preoperative information about difficulty in emptying the bladder constitutes a predisposing factor and may require preoperative elucidation and treatment. Postoperative retention of urine may be countered by informative and practical measures and restriction of fluid intake. In selected cases, prophylactic treatment with alpha-blockers and prostaglandin may reduce the frequency. Therapeutically, oral parasympathomimetica do not appear to be effective while alpha-blockers may be employed. In cases where catheter treatment is employed and which is anticipated to be required for more than 48 hours, suprapubic drainage is recommended as this results in fewer cases of urinary infection than transurethral indwelling catheters.(ABSTRACT TRUNCATED AT 250 WORDS)