Background: The assessment of schizophrenia in autistic people with intellectual disabilities is challenging. This study aimed to explore the identification of schizophrenia in this population. Methods: Using data from a clinical multi-centre study, reported symptoms in 26 autistic individuals with intellectual disabilities diagnosed with co-occurring schizophrenia were explored. Scores on two checklists (Psychopathology in Autism Checklist [PAC], Aberrant Behaviour Checklist [ABC]) were compared with two comparison groups: autistic individuals with intellectual disabilities and other mental disorders (94), or no mental disorder (63). Results: Reported symptoms of schizophrenia in this population met the formal diagnostic criteria. For PAC/ABC scales, only PAC psychosis differed for the schizophrenia group. Among participants with schizophrenia, two were diagnosed with additional mental disorders. Elevated scores for anxiety and depression were common. Conclusions: Emphasising core symptoms seems necessary when assessing co-occurring schizophrenia in autistic people with intellectual disabilities. The PAC may serve as a helpful screening tool.