The use of an observational assessment instrument designed for autistic children is described. The Behavior Rating Instrument for Autistic and other Atypical Children (BRIAAC) measures behavior in eight developmental areas: relationship to an adult, communication, drive for mastery, vocalization and expressive speech, sound and speech reception, social responsiveness, body movement, and psychobiological development. A case study of an autistic child is presented focusing on behavioral change over an 18 month period. Implications for using the BRIAAC and the course of behavioral change in autistic children are discussed. (Author/CL)