Adults with autism and intellectual disability (ID) are assumed to have high vulnerability for developing psychiatric disorders, but instruments or criteria for identifying those who may be in need of psychiatric services have been lacking. This study presents a new carer-completed screening checklist designed for this purpose. Differentiation between symptoms related to autism and to psychiatric disorders is indicated in order to identify psychiatric disorders in persons with autism. The Psychopathology in Autism Checklist (PAC) contains 30 items representing symptoms previously evaluated as specific to one of four major psychiatric disorders (psychosis, depression, anxiety and OCD) and not related to autism. Twelve items evaluated as indicators of general adjustment problems are also included. All 42 items are based on ICD-10 and DSM-IV criteria. The PAC was piloted on a sample of 35 adults with autism and ID. The score of participants previously identified with co-occurring psychiatric disorders (i.e. psychosis, depression, anxiety disorder, or OCD) were compared with the score of participants without psychiatric disorders. The results indicate acceptable psychometric properties, and that the PAC discriminates between adults with autism and ID with and without psychiatric disorders, and partially between individuals diagnosed with different psychiatric disorders. (Contains 5 figures and 6 tables.)