This multicenter, randomized, double-blind, placebo-controlled study evaluated the analgesic efficacy and opioid-sparing effects of valdecoxib, a potent COX-2 specific inhibitor, in patients undergoing knee replacement. Patients received morphine by patient-controlled analgesia (PCA), and valdecoxib 40 mg or 80 mg daily, or placebo, for up to two days. Efficacy was assessed by the cumulative amount of morphine administered over 48 hours, pain intensity and patient's evaluation of medication. Morphine consumption over 48 hours by patients receiving valdecoxib 40 mg or 80 mg daily plus morphine was 83.7% and 75.8% (P < 0.05) of the total amount consumed by patients receiving morphine alone. Patients receiving valdecoxib 40 mg and 80 mg daily experienced significantly lower maximum pain intensity on Day 2 (P < 0.05), and rated their study medication significantly higher than patients receiving morphine alone. Valdecoxib plus morphine was well tolerated. Thus, valdecoxib in combination with morphine provides multi-modal analgesia that reduces pain and opioid use and increases patient satisfaction following knee replacement surgery.