Despite the fact that opioid analgesics represent the mainstay for the treatment of postoperative pain in children, little attention has been directed toward measuring the incidence and intensity of opioid-induced side effects Given the potential for opioid-induced side effects to occur, techniques for precise measurement of these side effects in children need to be evaluated This paper critiques various approaches used to measure four of the most clinically significant opioid-induced side effects in children, namely, alterations in mental status and motor function, respiratory depression, and cardiovascular changes.