RESUMO
BACKGROUND: The assessment of functional impairment is crucial both for the diagnosis and the therapeutic approach to autism spectrum disorder (ASD). The purpose of the present study was to evaluate whether the FAST is a reliable and valid tool to assess functional impairment in adults with Level 1 ASD and to study the differences in psychosocial functioning between younger and older adults with ASD. METHODS: A case-control study was carried out in a sample of 150 participants, 71 adults with Level 1 ASD, and 79 adults without psychiatric history records. RESULTS: Results showed good psychometric properties in terms of validity and reliability. Cronbach's alpha for the total scale was .91 and the area under the curve was .98. The study also showed that adults with ASD present different profiles of functional impairment depending on their age: while younger patients present greater impairment in autonomy, older patients show more difficulties in interpersonal relationships. CONCLUSIONS: Our results support the use of the FAST in the evaluation of adaptive functioning in adults with Level 1 ASD.