The UK government identified ‘improving support within the criminal justice systems’ as a priority for autistic people. There is a lack of quantitative research to enable policymakers to make evidence-based decisions on how to improve access to justice for autistic people. This study used a case-comparison design to compare the experiences of 145 autistic and 116 non-autistic adults who had been arrested at some point in their life. Autistic participants were nearly five times more likely to state that they were not given an appropriate adult even though they believed they needed one and felt less able to communicate with the police. Autistic participants felt less able to cope with stress, twice as likely to have experienced meltdowns and five times more likely to have experienced shutdowns because of their criminal justice involvement. We conclude that there are inequalities that autistic people face when navigating the criminal justice system and the degree to which they can participate effectively in the justice process. This has an impact on their mental health. Policy recommendations are discussed based on this evidence.Lay AbstractMost autistic people will never experience being arrested or charged with a crime, however for those who do tend to be less satisfied with the way they were treated. The purpose of this study was to find out if autistic people are being disadvantaged by the criminal justice system if they are arrested. Previous research has shown that autistic people may have difficulties communicating with the police. This study builds on this knowledge by uncovering why autistic people may not feel able to communicate with the police and whether the police made any adjustments to help them. This study also measures the impact of being involved with the criminal justice system on autistic people’s mental health, such as stress, meltdowns and shutdowns. The results show that autistic people were not always given the support they felt they needed. For example, not all autistic people had an appropriate adult with them at the police station who could help to make sure they understood what was happening around them. Autistic people were also more likely to feel less able to cope with the stress and more likely to suffer meltdowns and shutdowns because of their involvement with the criminal justice system. We hope this study will help police officers and lawyers to better support autistic people if they become involved with the criminal justice system.