Prisons exist to enforce the requirements of the courts for custodial sentences. In so doing a balance must be struck between safety and security on the one hand, and respect for human dignity on the other. An important aspect of this is the right to health care and medical services, the principles of which are set out in various United Nations and European covenants, recommendations, and declarations. Practitioners working in prisons should be familiar with these statements and this guide discusses them and gives clear references for further reading. Translating these principles into the practice of health care within the prison environment can, however, present complex ethical dilemmas to prison healthcare practitioners when conflicting demands are made upon them. For example, the principle of privacy and confidentiality, which is fundamental in medical care, is not, of necessity, a feature of custodial care. This short guide is an attempt to guide practitioners through some of these situations with clear practical advice based upon medical ethics and international covenants. The prison practitioner faces extraordinary challenges peculiar to their work. They encounter a significantly high number of cases of drug abuse, the communicable diseases of AIDS, hepatitis B and C, and tuberculosis, and cases of psychiatric disorders, all of which are adversely affected by the overcrowded conditions in many prisons. This guide contains concise information on the main diseases and disorders affecting the prisoner's health which the practitioner must be familiar with. This guide will be of interest to all healthcare practitioners working within the prison system. Prison governors and custodial staff may also find it of interest to familiarise themselves with the work and complex role of the prison healthcare practitioner.