The use of patient-controlled analgesia (PCA) is an important method to treat pain, but concerns about its safety and device selection have been raised. This study examined nearly 10,000 PCA-related medication errors submitted to MEDMARX, a database that tracks medication information from participating hospitals. Investigators discovered that patient harm was associated with 6.5% of the errors, and the errors overall were reported across all phases of the medication process. The most common errors were related to improper dosage or quantity. An AHRQ WebM&M commentary discusses a case of a PCA overdose and the mechanisms to promote its safe use.