Background and objectives: This randomized controlled trial was designed to evaluate, first, whether intra- or postoperative music therapy could influence stress and immune response during and after general anaesthesia and second, if there was a different response between patients exposed to music intra- or postoperatively. Method: Seventy-five patients undergoing open hernia repair as day care surgery were randomly allocated to three groups: intraoperative music, postoperative music and silence (control group). Anaesthesia and postoperative analgesia were standardized and the same surgeon performed all the operations. Stress response was assessed during and after surgery by determining the plasma cortisol and blood glucose levels. Immune function was evaluated by studying immunoglobulin A (IgA) levels. Patients' postoperative pain, anxiety, blood pressure (BP), heart rate (HR) and oxygen saturation were also studied as stress markers. Results: There was a significantly greater decrease in the level of cortisol in the postoperative music group vs. the control group (206 and 72 mmol L-1 decreases, respectively) after 2 h in the post anaesthesia care unit. The postoperative music group had less anxiety and pain and required less morphine after 1 h compared with the control group. In the postoperative music group the total requirement of morphine was significantly lower than in the control group. The intraoperative music group reported less pain after 1 h in the post anaesthesia care unit. There was no difference in IgA, blood glucose, BP, HR and oxygen saturation between the groups. Conclusion: This study suggests that intraoperative music may decrease postoperative pain, and that postoperative music therapy may reduce anxiety, pain and morphine consumption. © 2005 European Society of Anaesthesiology.