Background: Limited evidence suggests that people with ID (ID) are overrepresented in prisons although prevalence rates of ID among prisoners vary significantly across studies, making it difficult to identify prevalence and assess existing need.

Method: A systematic review of relevant literature was conducted, and results were organized and compared in relation to study aims, design, measures used to screen for ID, sample, limitations and key findings.

Results: Existing international data suggest a prevalence of prisoners with ID between 7 and 10%. Most frequent coexisting health issues among this population are hearing and vision impairments, obesity, diabetes and a range of mental health disorders, notably anxiety and personality and conduct disorders.

Conclusion: More research is required on prevalence rates and associated comorbidities of ID within prison settings, taking into account the heterogeneity of the population with ID.