We studied a number of factors that may be associated with urinary retention, in particular the method of postoperative analgesia delivery, in 47 men and 69 women undergoing lower limb joint replacements. The following factors were studied: age, gender, height, weight, previous history of urinary retention, presence of symptoms suggestive of urinary tract obstruction, type of anaesthetic (general anaesthetic or spinal anaesthetic), type of postoperative analgesia (intramuscular or patient-controlled analgesia with morphine) and the total dose of morphine given. Urinary retention developed in 18.1% of patients. Stepwise logistic regression analysis was used to identify independent explanators of an increased probability of developing urinary retention. Three factors emerged - male gender, increasing age and the use of patient-controlled analgesia.