Drug misuse and hepatitis C are known to be endemic in Irish prisons. Using a grounded theory approach, this qualitative study sought to examine prisoners' views of drug injecting practices and harm reduction interventions in Dublin prisons. Thirty-one male prisoners were interviewed (16 injecting drug users and 15 non-injectors). Two themes relevant to drug use practices emerged. Respondents described increased health risks related to injecting drug use during detention and associated with a prison environment. These included: the low availability of heroin which encouraged a shift from smoking to injecting; the scarcity of injecting equipment which fostered sharing networks far wider than outside prison; inadequate injecting equipment cleaning practices; and the rent of needles and syringes in exchange for the drugs. Both non-injectors and injectors interviewed supported harm reduction interventions in prison and felt that the range of drug services available in prison should mirror those currently available in the community, although half opposed or had reservations about syringe exchange in prison. Prisoners viewed their time in prison as an opportunity to address substance misuse related problems; health professionals should not miss this opportunity.