The purposes of this study were to compare the reliability and validity of three pain measurement scales for assessing pain in preverbal and nonverbal children and to determine which of the scales was most appropriate in a clinical setting to evaluate pain for infants and young children regardless of developmental stage or cognitive or physical disability. Pain scales tested were revised versions of the Riley Infant Pain Scale (RIPS), the Nursing Assessment of Pain Intensity (NAPI), and the Postoperative Pain Score (POPS). Purposive sampling of 391 postoperative infants and children was used for evaluation of pain in a midwestern children's hospital. Four assessments with each scale were done 1 hr apart by trained observers blinded to pain medications. Data analyses supported high inter-rater reliability, satisfactory discrimination between pain and no-pain observations, and suggested acceptability for all three scales with lower caregiver burden for RIPS and NAPI.