BACKGREOUND: Despite many advantages of spinal anesthesia, hypotension after spinal anesthesia is a common complication. The practice of routine preemptive infusion of crystalloid before spinal anesthesia has been widespread acceptance. But the value of this practice has recently been questioned. This study was designed to determine whether preoperative administration of crystalloid decrease the incidence of hypotension after spinal anesthesia. METHODS: Thirty ASA I and II patients for elective lower extremities operations under spinal anesthesia were randomized to receive either 500 ml Ringer's lactate solution prior to induction of spinal anesthesia (group I) or no prehydration (group II). Hypotension was defined as a 30% decrease from baseline systolic blood pressure or systolic <90 mmHg, and was treated with ephedrine 5 mg IV boluses. RESULTS: The incidence of hypotension was not significantly different between the two groups. Baseline systolic blood pressure significantly decreased after 5 min in the group I, 1 min in the group II, after induction of spinal anesthesia. The ephedrine dose requirement to maintain systolic pressure >70% of baseline, systolic blood pressure and heart rate were not significantly different between both groups. CONCLUSIONS: We conclude that, in normovolemic adult patients undergoing elective lower extremities surgery, an intravenous infusion of 500 ml of Ringer's lactate solution is ineffective in preventing hypotension during spinal anesthesia.