The paper describes the reasons for developing a new instrument to measure adaptive behavior of mentally retarded residents at Glenwood State Hospital-School and recounts the processes involved in constructing the new scale. Among complaints about the American Association on Mental Deficiency Adaptive Behavior Scale (ABS) are its inappropriateness with very low functioning persons and item arrangement and scoring. A review of specific items was carried out, and a factor analysis was performed using data gathered from administering the ABS to 200 redidents. The factor analysis was designed to determine the best arrangement of the items into domains. Results suggested that the six factors could be better conceptualized in two broad categories, first, those having to do with general abilities or behaviors (cognitive and communication skills and social responsiveness), and second, those relevant to specific behaviors (basic self-help skills, self-care skills, and community living skills). Tables listing adaptive and maladaptive behavior factor items and the percent of variance accounted for by each conclude the paper. (CL)