Adults with Intellectual disability (ID) and Autism Spectrum Disorder (ASD) are more vulnerable to mental health problems than the general population.

This study investigates presence and rate of psychiatric disorders in comparison with ID or ASD alone, and appropriateness of assessment and diagnostic procedures or tools.

A systematic mapping of the literature was carried out on the basis of the above mentioned issues. The search was conducted using PubMed and ScienceDirect, according to the following keywords: psychiatric comorbidity, psychiatric disorders, autism, ASD, intellectual disability, mental health problems, adults, assessment tools, diagnosis. Twenty-eight papers were selected for pertinence to mapping issues among more than 500.

Many studies show that ASD is an important vulnerability factor for psychiatric co-morbidity and for challenging behaviors (CBs) in adults with ID. Highest rates were reported for psychotic, mood, anxiety, and obsessive-compulsive disorders. Few studies show that the difference between adults with ID plus ASD and adults with only ID are not statistically significant, but for the presence of CBs in those with ID plus ASD. The disagreement of results is based on a variety of factors such as diagnostic over-shadowing, scarcity of specific assessment tools, consideration of the introspective and communication difficulties, incompleteness of medical records, and low reliability of information sources.

Although low studies concordance, the literature mapping suggests the presence of ASD in ID to be associated with higher rates of psychopathology. Since the relevant implications for prevention and clinical management, further research with high-level evidence is hoped.

The authors have not supplied their declaration of competing interest.