INTRODUCTION: Urinary retention (UR) is one most common complication of anal surgery and its cause is multifactorial. Postdural puncture headache (PDPH) is caused by cerebrospinal fluid leakage after spinal anesthesia, therefore it may be aggravated by early ambulation. PURPOSE: To determine whether early ambulation (EA) vs. bed rest (BR) reduces the incidence of UR after anal surgery under spinal anesthesia, without causing PDPH. METHODS: In this prospective, randomized study, 107 patients undergoing anal surgery under spinal anesthesia were randomly assigned in the EA group (n=54) or the BR group (n=53). UR was defined as a voiding difficulty that needs catheterization. In the BR group, the patients were positioned flat in bed on the operation day. Anesthetic techniques (tetracaine injection using 24-gauge needle in sitting position, bupivacaine local infiltration) and postoperative pain therapy (intramuscular demerol injection every 6 hours, oral nonsteriodal antiinflammatory drug plus acetaminophen) were standardized. Perioperative intravenous fluids were restricted. RESULTS: Urinary retention and PDPH occurred in 32 (29.9%) and 7 (6.5%) patients, respectively. UR was significantly reduced in the EA group (10/54=18.5%) vs. the BR group (22/53=41.5%) (p=0.017, Chi-square). The incidence of PDPH, however, was not different between the two groups (5.6% in the EA vs. 7.5% in the BR group). CONCLUSIONS: Early ambulation has important implication on reducing the incidence of urinary retention after anal surgery under spinal anesthesia, without causing PDPH.