The Autism Diagnostic Observation Schedule, Second Edition (ADOS-2), Module 4 is considered a “gold-standard” instrument for diagnosing autism spectrum disorder (ASD) in adults. Although the ADOS-2 shows good sensitivity and specificity in lab-based settings, it is unknown whether these results hold in community clinics that serve a more psychiatrically impaired population. This study is the first to evaluate the diagnostic accuracy of the ADOS-2 among adults in community mental health centers (n = 75). The ADOS-2 accurately identified all adults with ASD; however, it also had a high rate of false positives among adults with psychosis (30%). Findings serve as a reminder that social communication difficulties measured by the ADOS-2 are not specific to ASD, particularly in clinically complex settings.