This chapter provides a review of the data available in Ireland on drug-related infectious diseases (hepatitis B, C and HIV). These diseases continue to be an issue of major concern in relation to Irish injecting drug users. The section on determinants of drug-related infectious diseases in the Irish context presents an overview of research that has looked at the risk behaviours engaged in by Irish drug users, both in relation to their injecting drug use and their sexual behaviour. It also explores the data available on both the health-related consequences and the wider social consequences of drug-related infectious diseases. An outline of the harm-reduction services available to Irish injecting drug users, which aim to prevent the spread of drug-related infectious diseases among this population, is given. Services that provide care for those already infected are also described. The authors identify a number of gaps in the information available in this field including, the absence of comprehensive routine data collection on the diseases and a lack of research on the societal and familial consequences of the diseases.