Attitudes to treating moderate to severe pain in infants have changed during the past 15 years. Previously, strong analgesia was often withheld because of worries about unwanted effects of the drugs in sick infants, and because it was mistakenly believed that very young infants do not feel or remember pain. The need to prevent and relieve pain in infants is now widely accepted. In this article we review pain relief in the very young, concentrating on the recognition and treatment of acute pain such as occurs with surgery, invasive procedures, injury or acute inflammation. A future article will discuss the assessment and relief of pain in older children.