The Autism Diagnostic Observational Schedule (ADOS) is a semi-structured observational scale developed to assess social interaction, communication and play in individuals who are suspected to have autism. Since the ADOS is not suitable to be used with severely or profoundly mentally retarded adolescents and adults with very limited language skills, materials and some of the tasks of the PL-ADOS and the original ADOS (the former versions of the current ADOS) were adapted. Results indicated that almost all of the overall ratings showed good reliability and discriminative diagnostic validity. Furthermore, the combination of codings into an overall algorithm score on social/communicative behavior resulted in a sensitivity of 0.82 and a specificity of 0.85 when using a cut-off score of 15.