We retrospectively studied 279 patients who had undergone uncomplicated open appendectomy for acute appendicitis to determine risk factors for postoperative urinary retention. The gender of the patients, the operating time and the amount of fluid given perioperatively had no influence on the occurrence of retention. The amount of analgesic agent administered postoperatively and the age of the patient were significantly associated with urinary retention (p = 0.01 and p < 0.0001, respectively, after adjustment for potential confounding factors). The use of meperidine hydrochloride as compared with morphine and of patient-controlled analgesia as compared with intramuscular delivery were initially found to be significantly related to retention (p = 0.014 and p < 0.0001, respectively). After the effects of the age of the patient, the drug type and the amount of fluid and analgesic agent administered were controlled for, patient-controlled analgesia remained significantly associated with retention (p < 0.0001), whereas the type of drug given was no longer significant after controlling for potential confounding factors. Because we found that urinary retention was 13 times more likely to occur in the patients who had patient-controlled analgesia, we recommend that the use of this form of analgesia delivery be avoided after open appendectomy.