There are more than 10 million people imprisoned worldwide. These individuals experience a higher burden of communicable and non-communicable disease, mental health and substance misuse problems than the general population and often come from marginalized and underserved groups in the community. Prisons offer an important opportunity for tackling health problems in a way that can deliver benefits to the individual and to the community. This paper focuses specifically on emerging health issues for prisons across the world. This paper uses sources of international data from published systematic reviews and research studies, the Ministry of Justice for England and Wales, the Prisons and Probations Ombudsmen Review and other United Kingdom government briefing papers. Deaths in custody are a key concern for the justice system as well as the health system. Suicide is the leading cause of mortality in prisons worldwide but non-communicable diseases, such as cardiovascular disease, are increasing in importance in high-income countries and are now the leading cause of mortality in prisons in England and Wales. The prison population is ageing in most high-income countries. Older people in prison typically have multiple and complex medical and social care needs including reduced mobility and personal care needs as well as poor health. Further research is needed to understand the complex relationship between sentencing patterns, the ageing prison population and deaths in custody; to model its impact on prisons and healthcare provision in the future and to determine effective and cost-effective models of care. Research into the health of prisoners is important in improving the health of prisoners but there is considerable variation in quantity and quality between countries. Recent innovations seek to address this disparity and facilitate the sharing of good practice.