The MESSIER, a measure of social and communication skills and the Vineland Social Maturity Scale were administered to 618 severe and profoundly mentally retarded adults. The goal of the study was to establish the potential utility of the MESSIER for classifying level of intellectual disability in this group. Comparing MESSIER scores to previously established DSM-IV-TR diagnosis, 86% of the severe and 80% of the profoundly mentally retarded persons were correctly classified. The implications of these data in using the MESSIER for classification and treatment planning are discussed.