The Autism Diagnostic Observation Schedule (ADOS) is a semi-structured, standardized observational assessment that is widely used in research and clinical services. It is organized into four modules based on age and language. However, Module 4 is the only module designed for adults, is limited to use with verbally fluent individuals, and its diagnostic algorithm is not comparable to other ADOS Modules. Modules 1 and 2, appropriate for children with limited language, are not validated in adult samples. The proposed study seeks to adapt autism diagnostic tools to be appropriate for use with adults of all levels of verbal ability and use these measures to describe trajectories in ASD. An adapted version of Modules 1 and 2 for adults with limited language is being piloted at the University of Michigan; other sites will begin piloting in summer 2010. Data will be used to create diagnostic algorithms and calibrate severity scores. Analyses to revise the Module 4 algorithms and create a severity metric will use an existing dataset combined with participants recruited for this project. To explore trajectories in ASD, severity scores will be applied to a longitudinal sample that has been followed from age 2 into adulthood. The development and refinement of autism diagnostic instruments for use with adults of varying levels of verbal skills will facilitate future efforts to understand the manifestation of ASD across the lifespan. The calibrated severity metric may also be useful in investigations seeking to link neurobiological functioning to ASD-related symptoms.