This publication sheds light on the situation of drug users among criminal justice populations and corresponding health care responses in nine countries in Eastern and South-East Europe and Kosovo. In many of the studied prison systems there is an almost complete unavailability of effective addiction treatment – e.g. opiate agonist treatment (OAT) – or the potential of such treatment has not yet been fully exploited. Detoxification treatment alone or interruption of treatment can have negative effects on the health of drug-dependent persons. However, some places have been applying state-of-the-art addiction treatment and harm reduction measures, including needle and syringe exchange programmes, for quite some time.