The pathophysiology, assessment, and pharmacologic management of acute pain in infants and children are reviewed, and the mechanism of action, pharmacokinetics, clinical efficacy, adverse effects, and dosages of opioid analgesics, nonopioid analgesics, and local anesthetics used for regional blocks are discussed. The pathophysiology of pain and the physiologic rationale for treatment of pain are similar in children and adults. Severe pain can be controlled by i.v. or epidural administration of opioid analgesics. Neonates are more susceptible to the depressant effects of opioids, and opioid analgesia must be administered with caution in infants who are not receiving mechanical ventilation because of the associated risk of respiratory depression. Patient-controlled analgesia is a useful technique in older children. Acetaminophen and NSAIDs are useful for relieving milder pain of noninflammatory and inflammatory origin, respectively. Epidural or intrathecal administration of local anesthetics provides regional analgesia with minimal physiologic alterations. Topical application of local anesthetics is effective for many minor procedures. A variety of pain management techniques are available for the management of acute pain in pediatric patients. The development of drugs having fewer adverse effects and noninvasive administration techniques will be important research priorities in the coming years.