The study analysed data from 295,734 individuals in Stockholm County, Sweden, of whom 5,739 had a diagnosis of autism. The researchers tracked these individuals for violent crime convictions between ages 15 to 27 years using records from the Swedish National Crime Register.

The team, led by researchers at University of Bristol’s Population Health Science Institute and the Karolinska Institute in Stockholm, found that individuals diagnosed with autism initially appeared to have a higher risk of violent offending. However, this risk was significantly reduced once the presence of additional attention-deficit/ hyperactivity disorder (ADHD) or conduct disorder were taken into account.

The study reported that having these co-occurring conditions, along with other, later-onset psychiatric disorders and alcohol and drug misuse, were the most important individual predictors of violent criminality in autism, not autism by itself.

Interestingly, when researchers considered individuals with ADHD or conduct disorder, an additional diagnosis of autism was actually found to reduce the risk of violent criminality, compared to individuals with ADHD or conduct disorder alone.

Dr Ragini Heeramun, Consultant Forensic Psychiatrist at the Avon & Wiltshire Partnership NHS Mental Health Trust in Bristol, said:

“We know that some people with an autism diagnosis have challenging behaviour and may come into contact with the criminal justice system, however, whether having autism increases the risk of violence or not has previously not been clear.”

“Our findings, from the largest study to date, show that at the population level, autism in itself doesn’t seem to be associated with convictions for violent crimes. However, other conditions, such as ADHD, which can co-occur with autism, may increase such risks.” 

Dr Dheeraj Rai, Consultant Senior Lecturer in Psychiatry at the University of Bristol, said:

“Interestingly, the additional presence of an autism diagnosis with attention-deficit/ hyperactivity disorder (ADHD) or conduct disorder was actually associated with a relatively lower risk of convictions, compared to having these conditions without autism.”

“These findings are important for autism services, which often focus on providing a diagnosis of autism, rather than the identification of, and support for, the conditions that commonly occur alongside it.”

Richard Mills, Research Director, Research Autism, said:

“This an important study, which confirms that autistic individuals are no more likely to commit violent crime than the general population, after accounting for other conditions like ADHD.

“That it is a population study and not a study of an existing offender or clinical population adds weight to the findings. 

“The presence of neurological conditions such as ADHD in offender populations should always be considered as these are significant risk factors in offending across the board and are known to co-occur with autism.”

Dr James Cusack, Director of Science, Autistica, said:

“This study rejects the myth that autism is related to criminal violent behaviour. Interestingly, getting a timely diagnosis lowered the likelihood of violent behaviour showing, yet again, why it's vital to make sure everyone gets access to high quality diagnostic services and appropriate support. 

“It was found that violent behaviour was only elevated in autism when co-occuring conditions such as ADHD and Conduct Disorder were also present. At Autistica we're investing in new studies to find better ways to manage co-occurring conditions like this in autism.”