BACKGROUND: The purpose of our study was to evaluate whether, by varing the duration of lateral decubitus, subarachnoid administration of hyperbaric bupivacaine in a lateral decubitus position could produce a differential spread between the dependent and nondependent sides, and also to determine the clinical advantage of this procedure. METHODS: In a lateral position with the operating side dependent, all patients received 15mg of hyperbaric 0.5% bupivacaine and were randomized into four groups according to the duration of lateral decubitus after subarachnoid injection: Group I: patients immediately turned supine after the injection, Group II: 5 min in lateral decubitus position after the injection, then supine, Group III: 10 min in lateral decubitus position after the injection, then supine, Group IV: 15 min in lateral decubitus position after the injection, then supine. The maximum sensory block level using pinprick test, the time to maximum sensory block, the duration of sensory block, the time to complete motor block and the duration of complete motor block in the dependent and nondependent sides were measured. RESULTS: There were no statistical difference in maximum sensory block level, duration of sensery block, and duration of complete motor block between both sides in the same group nor among four groups. CONCLUSIONS: In conclusion, there was no significant influence of lateral decubitus on the spread of hyperbaric bupivacaine and the present study does not demonstrate any clinical advantage of a prolonged lateral position for 15 min after subarachnoid injection.