Previous studies have demonstrated reduced postoperative morphine requirements and/or improved pain relief when nonsteroidal antiinflammatory drugs are administered in conjunction with patient-controlled analgesia (PCA). This double-blind study aimed to determine whether these effects could be obtained with a sustained-release ibuprofen formulation (Brufen Retard®) given preoperatively, obviating the need for oral administration during the early postoperative period. We aimed also to determine whether the anticipated reduction in morphine requirements was associated with reduced opioid side effects. One hundred fifteen patients scheduled for lower abdominal gynecological surgery were randomly assigned to receive either sustained-release ibuprofen, 2 x 800 mg (n = 57), or placebo (n = 58) preoperatively and again 24 h after the first dose. Arterial oxyhemoglobin saturation (SpO2) was monitored preoperatively and for 24 h postoperatively. Patients were assessed every 4 h up to 24 h postoperatively. Those receiving ibuprofen reported significantly less pain at rest (P = 0.023) and less pain on movement, although the latter was not statistically significant (P = 0.051). Patients' opinions of the efficacy of their pain-relieving medication (P < 0.001) and quality of sleep (P = 0.036) favored ibuprofen. Morphine consumption was slightly but not significantly lower in the ibuprofen group (32 vs 38 mg/24 h, P = 0.096). SpO2 (P = 0.54), level of consciousness (P = 0.65), and number of antiemetic administrations (P = 0.15) did not differ significantly between groups. These results demonstrate improved efficacy with no increase in side effects when sustained-release ibuprofen is used as an adjunct to morphine PCA.