ABSTRACT Objective The primary aim of the study was to ascertain the usefulness and the validity of the set of criteria proposed to define a subgroup within the DSM-III-R category of pervasive developmental disorder-not otherwise specified under the name of multiple complex developmental disorder (MCDD). Method A multivariate analysis (cluster and principal-components analysis) was performed on the characteristics, reliably extracted from the charts of 105 children with MCDD, 32 with autistic disorder, 51 with externalizing disorders, and 56 with internalizing disorders, all with an 10 greater than 70, fully assessed in our department between 1984 and 1991. Results The main finding was a strong correspondence between the classification of the cases by DSM-III-R categories and the subdivision by means of a multivariate cluster analysis. The cluster analysis did not discriminate between children with emotional and disruptive disorders. Furthermore, children with MCDD and autistic disorder were significantly different both on symptom factors (“psychotic thinking/anxiety,” “aggression,” “deficient interaction/communication,” “stereotyped and rigid behavior,” and “suspiciousness/odd interaction”) and on factors that reflected developmental and environmental background variables. Conclusions The results of this study add to the nosology of autistic spectrum disorders and lend additional support to the need for a separate subcategory of MCDD within DSM-V. Further corroboration of these results in independent (multicenter) samples will be required. J. Am. Acad. Child Adolesc. Psychiatry, 1995, 34, 8:1096–1106.