Anger expression styles are associated with psychological and physical well-being among adults. Little is known about the role of anger expression in children's functioning. This lack of knowledge has resulted, in part, from a lack of validated tools for anger expression measurement. The Pediatric Anger Expression Scale-3rd edition (PAES-III; Jacobs, Phelps, & Rohrs, 1989; Jacobs & Kronaizl, 1991) has been proposed as a reliable and valid assessment instrument of anger expression styles. The PAES-III includes three scales that measure anger turned inward, anger expressed outwardly, and anger controlled cognitively or behaviorally. We evaluated the psychometric properties of this instrument when it is administered verbally to children with juvenile rheumatoid arthritis, children with juvenile diabetes mellitus, and healthy children. Internal consistency was adequate for anger-in and anger-out, but marginal for anger-control. Concurrent validity was supported for the total sample. A principal components analysis suggested a four-factor model of anger expression. Overall, the PAES-III was found to have psychometric limitations. Use of a modified PAES-III may facilitate pediatric behavioral medicine research addressing risk factors for maladjustment among children with chronic illnesses.