This chapter focuses on the process by which deviant behavior is officially defined as a medical problem. I present an analysis of how children are diagnosed as hyperactive at the HA-LD clinic of Northeastern Pediatric Hospital Medical Center (NPH). The analysis views the construction of a medical reality (diagnosis) of hyperactivity or hyperkinesis as problematic for the actors (physicians and other medical personnel) in the clinic situation and as the outcome of an interpretive social process. It is problematic in that children are usually referred to the clinic for deviant behavior ("learning and behavior problems") rather than manifestly medical problems and to diagnose hyperactivity the physicians must construct a medical reality. This process is full of uncertainties for the physicians (cf. Conditions of Uncertainty at the HA-LD Clinic below). a In fact, I contend the central issue in the construction of the medical reality of hyperactivity is the minimization of uncertainty. Uncertainty is minimized through the interpretive social process of evaluation and examination.