Patient-controlled analgesia (PCA) is a relatively new technique in which patients are able to self-administer small doses of opioid analgesics when needed. Many different devices are available for opioid infusion, including a syringe pump, disposable plastic cylinder, and battery-operated computer-driven pump. These devices allow patients to choose an intermittent (demand) bolus, continuous infusion, or both modes of administration. Parameters, such as route, drug concentration dose, frequency, and maximum daily or hourly dose, are programmed by the physician. The patient decides whether or not to take a dose. Devices can be used to deliver the drug into a running intravenous infusion, the epidural space, or subcutaneously. Controlled trials indicate that PCA is probably superior to regular opioid administration in postoperative pain. Reported advantages include greater patient satisfaction, decreased sedation and anxiety, and reduced nursing time and hospitalization. Preliminary experience suggests that PCA is also useful and safe for cancer pain, but further research is greatly needed.