Although social work scholars have proposed and promoted various models for making effective and ethical clinical decisions, little empirical research has addressed processes of clinical decision-making as they occur naturally in ‘real world’ mental health practice. This article briefly reviews approaches to the study of decision-making, and presents findings from an ethnographic study of the collaborative decision-making activities of mental health workers in a residential treatment center for children and adolescents. This article describes and analyzes a local theory and practice of interactional clinical decision-making in which workers provide competing interpretations of the ‘meaning’ of clients’ behaviors before committing to a particular course of clinical action. This process, which I term the ‘behavior-has-meaning’ hermeneutic, serves not only to guide clinical interventions, but as a forum for modeling, developing, and evaluating locally valued forms of clinical expertise. Implications of these findings for the implementation of prescriptive models of clinical decision-making – such as the evidence-based practice process – are discussed.