OBJECTIVE: To evaluate and compare the analgesic efficacy and adverse effects of tramadol and pethidine in labor. METHOD: Fifty-nine full term parturients were randomly assigned to one of two groups in active labor. Group 1 received 100 mg pethidine; group 2, 100 mg tramadol, intramuscularly. Analgesic efficacy, maternal side effects, changes in the blood pressure, heart rate, and duration of labor were assessed. RESULT: At 30 and 60 min after drug administration, pain relief was greater in the pethidine group than in tramadol group. The incidence of nausea and fatigue was higher in the tramadol group. Following drug administration the decrease in systolic and diastolic blood pressure and the increase in heart rate were statistically significant in both groups. No significant difference was found between the groups when compared for duration of labor and Apgar scores. None of the neonates developed respiratory depression. CONCLUSION: Pethidine seems to be a better alternative than tramadol in obstetric analgesia because of its superiority in analgesic efficacy and low incidence of maternal side effects.