BACKGROUND: Urinary retention is one of the most common complications after spinal anesthesia, and its inadequate management can result in serious outcomes. Overdistended bladder due to urinary retention should be catheterized. This study determined whether the prophylactic medication of oral bethanechol, a parasympathomimetic drug, results in reduction in the frequency of catheterization due to urinary retention. METHODS: Twenty-seven healthy male patients undergoing lower extremity operation under spinal anesthesia were subjected and randomly allocated into three groups according to the drug which was given. Group I (n = 9) had no medication, Group II (n = 9) and Group III (n = 9) were given bethanechol 50 mg or bethanechol 100 mg orally, respectively, before anesthesia. We measured the number of catheterized patients, the frequency of catheterization per catheterized patient, and perioperative cardiovascular complications in each group after their operations. RESULTS: The number of catheterized patients was nine (100%) in Group I, three (33%) in Group II, and two (22%) in Group III (P < 0.002). There was a significant statistical difference among the groups (P < 0.002). As the dosage of bethanechol increased, its effect increased relatively (P < 0.001). CONCLUSIONS: Prophylactic oral medication of 50 100 mg bethanechol reduces the frequency of catheterization in urinary retention after spinal anesthesia.