During the postoperative period, the efficacy of opioid treatment is different among patients. Indeed, an extreme variability exists between patients, concerning their analgesic requirement and their sensibility to opioids. To improve opioid analgesia, some empiric considerations must be observed: 1) Techniques of opioid administration must allow to titrate analgesic requirement. Patient Controlled Analgesia represents a real improvement and should be developed. 2) Occurrence of side effects must be avoided. The combination of different analgesics must be prescribed systematically, if there is no contraindication. 3) Opoid side effects must be appropriately treated, in order to improve the quality of analgesia. These simple measures require regular evaluation of opioid analgesia, and treatment of the side effects.