Depressive disorders are common in autistic adults, but few studies have examined the extent to which common depression questionnaires are psychometrically appropriate for use in this population. Using item response theory, this study examined the psychometric properties of the Beck Depression Inventory-II (BDI-II) in a sample of 947 autistic adults. BDI-II latent trait scores exhibited strong reliability, construct validity, and moderate ability to discriminate between depressed and nondepressed adults on the autism spectrum (area under the receiver operating characteristic curve = 0.796 [0.763, 0.826], sensitivity = 0.820 [0.785, 0.852], specificity = 0.653 [0.601, 0.699]). These results collectively indicate that the BDI-II is a valid measure of depressive symptoms in autistic adults, appropriate for quantifying depression severity in research studies or screening for depressive disorders in clinical settings. A free online score calculator has been created to facilitate the use of BDI-II latent trait scores for clinical and research applications (available at https://asdmeasures.shinyapps.io/bdi_score/).