This prospective, randomized double-blind trial was carried out to compare the postoperative analgesic efficacy and adverse profile of 0.1 mg and 0.2 mg intrathecal morphine in patients undergoing total hip arthroplasty. Patients were randomly divided into two groups: group I (n = 30) received 0.1 mg and group II (n = 30) received 0.2 mg. The patient, anesthesia and surgery related characteristics were comparable in two groups. The mean duration of analgesia (time to VAS = 4) and paracetamol consumption in group I and II were 18.52 +/- 3.14 vs 23.86 +/- 3.4 hours (p 0.05) and 7.57 +/- 0.57 vs 4.73 +/- 0.45 gram (p 0.05), respectively. Mean VAS scores at rest and active in both groups were less than 4 and similar at 48 hours after surgery. The frequency of nausea and vomiting, pruritus and urinary retention in group I and II were 13.3 percent vs 43.3 percent, 10 percent vs 20 percent (p 0.05), 16.8 percent vs 26.7 percent and 23.3 percent vs 30 percent (p 0.05), respectively. There was no significantly difference in patient satisfaction and sedation score between both groups and no case of respiratory depression was observed. In conclusion, 0.2 mg dose of intrathecal morphine produced longer postoperative analgesia but higher rate of nausea and vomiting than the 0.1 mg dose.