Objetives: The purpose of this study was to compare the analgesic efficacy and tolerability of opioids hydrocodone and tramadol in the relief of cancer pain. Methods: One hundred and eighteen patients with chronic cancer pain participated in a double-blind, randomized controlled trial. Sixty-two patients received hydrocodone and 56 patients received tramadol. Results: Hydrocodone/acetaminophen was effective in relieving pain in 56.5% of the patients at the starting dose of 25mg/2500 mg/d. An additional 14.5% of the patients responded to a double dose, and the remaining 29% of patients did not experience any pain relief from hydrocodone administration. One dose of tramadol at 200mg/d produced pain relief in 62% of the patients and alleviated pain in another 11% of patients at a dose of 400mg/d, and remaining 27% of patients did not experience pain relief from tramadol. No significant statistical difference in the analgesic efficacy of tramadol clorhydrate and hydrocodone/acetaminophen was found. The groups differed significantly in the incidence of side effects like nausea (P = 0.03; relative risk (RR), 1.69; confidence interval (IC) 95%, 1.03-2.77), vomiting (P = 0.02; RR, 2.21; IC 95%, 1.14-4.32), dizziness (P = 0.03; RR, 2.12; IC 95%, 1.17-3.86), loss of appetite (P = 0.02; RR, 3.27; IC 95%, 1.12-9.55) and weakness (P = 0.019; RR, 7.75; IC 95%, 0.98-61.05). Conclusions: There was no superior analgesic efficacy with the administration of hydrocodone/acetaminophen when compared to patients receiving tramadol in the relief of cancer pain. Tramadol produced more mild side effects than hydrocodone.