This article critically reviews the measures developed for assessing pain in the human neonate. Information was gathered with a computerized literature search of published articles and abstracts, a manual review of relevant conference proceedings, recently published journals, unpublished reports and manuscripts, and personal files. This identified 16 measures that were critically examined for their psychometric properties (reliability and validity) and clinical use. Special emphasis was placed on the feasibility of using neonatal pain assessment measures for clinical practice to address the research-practice gap. Although considerable progress has been made in the field of neonatal pain assessment, few measures have adequately established psychometric properties and clinical utility. Furthermore, most measures have been developed for research and not for the clinical setting. Issues regarding sensitivity, specificity, and the ability to detect clinically important changes have not been addressed. A sufficient number of infant pain measures have now been developed to assess acute pain. There is a paucity of measures to assess chronic pain in infants, and measures for infants who are low birth weight, critically ill, or ventilated. Future research should be aimed at strengthening the properties of existing measures, and at the development of measures for those infants with chronic pain or special needs.