Patient-controlled analgesia (PCA) via an infusion pump enables patients experiencing pain as a result of surgery, trauma or acute exacerbation of chronic conditions, to administer their own analgesia. Opioids are commonly used in the pumps because of their effectiveness and availability. This article, one of series on pain, describes the main features of opioid PCA, highlighting potential risks associated with this method of drug administration and common side effects of opioids. The article emphasises the importance of educating patients in PCA use to maintain safety. It is suggested that nurses must provide the same level of care to patients using PCA as patients receiving analgesia by other means.