The study assessed the diagnostic validity of the diagnostic behavioral assessment for autism spectrum disorders-revised (DiBAS-R; 19-item screening scale based on ratings by caregivers) in a clinical sample of 381 adults with ID. Analysis revealed a sensitivity of 0.82 and a specificity of 0.67 in the overall sample (70.3% agreement). Sensitivity (0.79) and specificity (0.84) were balanced in individuals with mild to moderate ID (83.3% agreement), while specificity was lower in individuals with severe to profound ID (sensitivity: 0.83, specificity: 0.34, 51% agreement). The level of ID as well as its interaction with ASD explained a significant proportion of the variance in the DiBAS-R scores. The DiBAS-R is an adequate screening tool, especially in individuals with mild to moderate ID.