To evaluate the reliability and validity of the FLACC Pain Assessment Tool which incorporates five categories of pain behaviors: facial expression; leg movement; activity; cry; and consolability. Eighty-nine children aged 2 months to 7 years, (3.0 +/- 2.0 yrs.) who had undergone a variety of surgical procedures, were observed in the Post Anesthesia Care Unit (PACU). The study consisted of: 1) measuring interrater reliability; 2) testing validity by measuring changes in FLACC scores in response to administration of analgesics; and 3) comparing FLACC scores to other pain ratings. The FLACC tool was found to have high interrater reliability. Preliminary evidence of validity was provided by the significant decrease in FLACC scores related to administration of analgesics. Validity was also supported by the correlation with scores assigned by the Objective Pain Scale (OPS) and nurses' global ratings of pain. The FLACC provides a simple framework for quantifying pain behaviors in children who may not be able to verbalize the presence or severity of pain. Our preliminary data indicates the FLACC pain assessment tool is valid and reliable.