Patient-controlled analgesia (PCA) is one of the newer techniques for pain management. It was developed in reaction to the large number of unsatisfied postoperative patients suffering from moderate to severe pain despite the availability of potent analgesic drugs. With PCA, patients are allowed to self-administer small analgesic doses into a running intravenous infusion, intramuscularly, subcutaneously or even into the spinal space. Clinical experience soon demonstrated that individual variability in pain intensity and analgesic needs was extremely large. Psychological factors seem to be as important as the surgical trauma. Opioid consumption is usually higher than with conventional regimens, but without serious side effects. Although patients generally prefer self-control, pain relief is not necessarily better than with well-conducted conventional techniques. In addition to routine clinical pain management, PCA has proven its importance in research, e.g. for pain measurement, to determine predictors of postoperative pain, to evaluate drug interactions and the concept of pre-emptive analgesia, or for pharmacokinetic designs. PCA has been extremely important in order to change the mind of physicians and nursing staff with respect to individual pain management strategies.