Traditional approaches to the study of children's expressions of anger rely on tightly controlled study environments to test hypotheses about outcomes and correlates of expression characteristics. An unexplored area in the study of emotion expression is a naturalistic examination of school-age children's spontaneously occurring expressions of emotion in their real, uncontrolled family contexts. This observational study describes the naturally occurring characteristics and contexts of 8- to 12-year-old children's anger expressions with family members. Thirty-one families were videotaped for 2 days at home and in community settings. Children's expressions of anger were identified and coded for angry facial, vocal and physical behaviors, and for the expressions' instigating situational contexts. The majority of anger expressions were of mild intensity and brief duration, and most often contained vocal behavioral characteristics (e.g., loud voice, whining). The most common cause of an anger expression was a verbal disagreement; other frequently occurring situational causes included homework, requests for compliance, and reprimands. Patterns in the angry behaviors children exhibited in response to specific situational causes support a functionalist perspective on emotion expression in that children engaged in behaviors that appeared to be attempts to get their needs met. Few differences were observed between mothers' and fathers' rates of instigating children's anger expressions, and between boys' and girls' expression characteristics and contexts. This study offers an ecologically valid, uniquely naturalistic methodology to describe children's observable expressions of anger as they occur in family contexts.