Background Injecting drug use is associated with increased morbidity and mortality. This is the first longitudinal study of a community-based population of injecting drug users (IDUs) in the Republic of Ireland.

Aim To establish the natural history of IDUs in a deprived Dublin community.

Methods Eighty-two IDUs (heroin) were recruited over the summer months of 1985. The prevalence of drug use in this district electoral area was established in 1985 and followed-up over a 25-year period with two formal interviews in 1995 and 2010.

Results It is a descriptive study of a cohort of IDUs established in 1985 prior to human immunodeficiency virus (HIV) testing being available. The majority of the cohort recruited included single, unemployed males aged 20 to 29 years, who had served a prison sentence. Fifty-one (63 %) of the cohort had died by 2010, of which 26 were attributed to HIV disease. The mean age of death was 35.9 years of age (standard deviation 4.1 years). Fifty-two (63 %) of the cohort tested positive for HIV and 58 (71 %) for hepatitis B between 1985 and 2010. The median survival time for those with a positive HIV status was 17 years (95 % CI 14.0–20.0) and for those with a positive hepatitis C status, 21 years (95 % CI 15.5–26.5).

Conclusions The lifestyle of IDUs, as demonstrated by the experience of this cohort, has hazardous consequences resulting in high levels of morbidity and mortality. A relatively stable picture of HIV associated with IDUs is now emerging in Ireland, as is the case throughout most of the EU. HIV is a more manageable chronic disease, posing challenges for primary care in its treatment of former and existing IDUs who are ageing and now have other chronic diseases.