This study describes an observational system (modified infant pain scale, MIPS) with elements from a previously published observational scale and from assessments of video-recorded infant facial expressions. It was designed to allow rapid and repeated assessments of pain in infants after brief training by an observer without pediatric experience. Forty healthy term infants (17 +/- 7 weeks) undergoing elective surgery had simultaneous independent assessment of pain using two scales: a naive observer used the MIPS and an experienced pediatric nurse used a 10-cm unmarked horizontal visual analogue scale (VAS). This validation of the MIPS included its division during analysis into partial (P-MIPS, without data on sleep or vital signs) and total scores. Infants had a broad range of MIPS scores, and the two scales categorized infants as "comfortable" or "not comfortable" with a high degree of concordance. The MIPS was easily incorporated into an infant's physical examination. We recommend its use for two-point clinical pain assessment.