Objectives:Spinal anesthesia has the advantage that profound nerve block can be produced in a large part of the body by the relatively simple injection of a small amount of local anesthetic. Intrathecal local anesthetics have limited duration. Different additives have been used to prolong spinal anesthesia. The effect of corticosteroids in prolonging the analgesic effects of local anesthetics in peripheral nerves is well documented. The purpose of this investigation was to determine whether the addition of dexamethasone to intrathecal bupivacaine would prolong the duration of sensory analgesia or not.Methods:We conducted a randomized, prospective, double-blind, case-control, clinical trial. A total of 50 patients were scheduled for orthopedic surgery under spinal anesthesia. The patients were randomly allocated to receive 15 mg hyperbaric bupivacaine 0.5% with 2 cc normal saline (control group) or 15 mg hyperbaric bupivacaine 0.5% plus 8 mg dexamethasone (case group) intrathecally. The patients were evaluated for quality, quantity, and duration of block; blood pressure, heart rate, nausea, and vomiting or other complications.Results:There were no signification differences in demographic data, sensory level, and onset time of the sensory block between two groups. Sensory block duration in the case group was 119±10.69 minutes and in the control group was 89.44±8.37 minutes which was significantly higher in the case group (P<0.001). The duration of analgesia was 401.92±72.44 minutes in the case group; whereas it was 202±43.67 minutes in the control group (P<0.001). The frequency of complications was not different between two groups.Conclusion:This study has shown that the addition of intrathecal dexamethasone to bupivacaine significantly improved the duration of sensory block in spinal anesthesia without any changes in onset time and complications.