DESIGN: The authors reviewed the available pediatric pain literature and selected those studies that reported quantitative information on the reliability and validity of, and the optimal cutoff points for, the visual analog scale (VAS) when used as an observational pediatric pain tool. RESULTS: Available psychometric findings concerning the observational VAS (VAS obs ) are limited. The estimated interrater reliability of the VAS (obs) from 9 studies ranged from 0.36 to 0.91. The correlation between self-report and the VAS (obs) was variable and ranged 0.23 to 0.83 in 6 studies. The concurrent validity of the VAS (obs) and other pain instruments ranged from 0.42 to 0.86. CONCLUSIONS: Further psychometric testing needs to be conducted on intraobserver reliability, responsiveness, and optimal cutoff points. Future research may guide the choice between VAS (obs) and the numerous behavioral pain instruments.