Pain assessments using three different observational pain assessment tools—the Post Operative Pain Score (POPS), the Nursing Assessment of Pain Intensity (NAPI), and the Pain Rating Scale (PRS)—were made on 98 preverbal children following surgery in an attempt to establish the reliability and validity of the three tools. Two observers (raters) scored pain intensity using each of the three instruments before and after administration of an analgesic. Interrater agreements were satisfactory on all three tools, with Interclass Correlations (ICC) ranging from. 71 to. 85.Ttests supported the discriminant validity of all three tools at thep<. 0001 level. The POPS and NAPI had internal consistency reliability alphas ranging from. 79 to. 88 for the POPS and. 59 to. 77 for the NAPI. Item analyses suggested specific revisions of the tools that might increase their reliability.