A child's pain is plastic and complex. In order to more effectively alleviate suffering, emphasis must shift from an exclusive focus on the source of tissue damage to a more comprehensive focus that includes factors that modulate pain. Evaluating a child's pain requires an integrated approach. Clinicians always should ask a child directly about his or her pain experience to determine the sensory characteristics. Clinicians also should assess situational factors to develop strategies to modify their impact. Then, a child's pain intensity should be measured regularly to monitor the effectiveness of interventions. Interviews, structured questionnaires, and simple rating scales are the primary tools to assess pain for most children older than 5 years of age. For infants, toddlers, and cognitively impaired children, physicians must infer the presence and severity of pain by evaluating changes in children's behavioral and physiological states. Parents and the health professionals who work most closely with children with particular handicaps can provide valuable information about the presence and severity of a child's pain because they often can recognize extremely subtle behavioral cues that indicate distress. A standardized but flexible approach is necessary to assess a child's pain. Pain assessment, like pain management, is a continuous process. Pain intensity rating scales should be used so children can provide a direct rating of their pain intensity and pain effect. Patients should receive some guidance about how to use the information from rating scales to develop consistent and objective criteria to know when children require analgesics and then to evaluate the effectiveness of those medications.