Patient-controlled analgesia (PCA) has successfully made the transitio
n from a research tool for the investigation of pain, to a wider clini
cal utility as method of pain control. Reliable and sophisticated PCA
systems have been commercially available for some time. The technique
has been most commonly used for control of postoperative pain, but has
also been successfully used during labour, after bums, in acute painf
ul medical conditions and in terminal care. It is generally more effec
tive than the traditional methods of postoperative pain control but no
t automatically so. The choice of opioid, the settings chosen for dema
nd dose and the lockout interval will greatly influence the effectiven
ess of this method of analgesia. Psychological variables are also impo
rtant in predicting the efficacy of PCA.