Purpose While individuals with an intellectual disability form a significant minority in the worldwide prison population, their healthcare needs require specialist attention. In Ireland, services for prisoners with intellectual disabilities need development. However, there is little substantive data estimating the prevalence of intellectual disabilities within the Irish prison system. The paper aims to discuss these issues. Design/methodology/approach The authors systematically review published data relating to the prevalence of intellectual disabilities in prisons in the Republic of Ireland. The authors searched four databases, governmental websites and corresponded with experts. Findings Little published data were elicited from searches except for one nationwide cross-sectional survey which reflected a higher prevalence than reported in international studies. Studies from forensic mental health populations are narrated to contextualise findings. Originality/value This study found that there is little data to accurately estimate the prevalence of intellectual disabilities in the Irish prison system and the limited data available suggests that this is likely to be higher than international estimates. The authors highlight the need for further research to accurately estimate prevalence in this jurisdiction, alongside the need to develop screening and care pathways for prisoners with an intellectual disability.