Objective:Shivering is an unpleasant sensation for patients who undergoing spinal anesthesia. This randomized double-blind clinical trial study was designed to compare the effect of intrathecal fentanyl with intrathecal meperidine for prevention of shivering in lower limb orthopedic surgeries under spinal anesthesia.Methods:Ninety patients were randomly recruited to receive either 3 ml of 0.5% hyperbaric bupivacaine plus 20 μg of fentanyl (Group F), or 3 ml of 0.5% hyperbaric bupivacaine plus 0.2 mg/kg of meperidine (Group M), or 3 ml of 0.5% hyperbaric bupivacaine plus normal saline (Group S). The incidence and intensity of shivering were compared in three groups. Data were analyzed by analysis of variances, Mann–Whitney U-test followed by Chi-square test.Findings:There were not statistically differences in complications and side-effects between three groups. Total incidence of shivering was similar between Groups F and M (16.7% vs. 13.3% respectively, P = 0.72) whereas it was significantly different to Group S (43.3%) (P = 0.025 for Group F vs. S, and P = 0.011 for Group M vs. S). Also the intensity of shivering between Groups F and M was similar (P = 0.66), while it was significantly less in these groups compared to Group S (P = 0.013 and P = 0.004, respectively).Conclusion:Addition of fentanyl 20 μg or meperidine 0.2 mg/kg to 0.5% bupivacaine intrathecally significantly decreased the incidence of shivering in lower limb orthopedic surgeries. There was no significant difference between two drugs with this respect.