People with severe mental illness and intellectual disabilities are overrepresented in the criminal justice system worldwide and this is also the case in Ireland. Following Ireland’s ratification of the United Nations’ Convention on the Rights of People with Disabilities in 2018, there has been an increasing emphasis on ensuring access to justice for people with disabilities as in Article 13. For people with mental health and intellectual disabilities, this requires a multi-agency approach and a useful point of intervention may be at the police custody stage. Medicine has a key role to play both in advocacy and in practice. We suggest a functional approach to assessment, in practice, and list key considerations for doctors attending police custody suites. Improved training opportunities and greater resources are needed for general practitioners and psychiatrists who attend police custody suites to help fulfill this role.