INTRODUCTION
People who inject drugs are at high risk of blood-borne infections. We describe the epidemiology of HIV among people who inject drugs in England, Wales, and Northern Ireland (EW&NI) since 1981.

METHODS
National HIV surveillance data were used to describe trends in diagnoses (1981-2019), prevalence (1990-2019), and behaviours (1990-2019) among people who inject drugs aged ≥15 years in EW&NI. HIV care and treatment uptake were assessed among those attending in 2019.

RESULTS
Over the past four decades, the prevalence of HIV among people who inject drugs in EW&NI remained low (range: 0.64%-1.81%). Overall, 4978 people who inject drugs were diagnosed with HIV (3.2% of cases). Diagnoses peaked at 234 in 1987, decreasing to 78 in 2019; the majority were among white men born in the UK/Europe (90%), though the epidemic diversified over time. Late diagnosis (CD4 <350 cells/µl) was common (2010-2019: 52% [429/832]). Of those who last attended for HIV care in 2019, 97% (1503/1550) were receiving HIV treatment and 90% (1375/1520) had a suppressed viral load (<200 copies/ml). HIV testing uptake has steadily increased among people who inject drugs (32% since 1990). However, in 2019, 18% (246/1404) of those currently injecting reported never testing. The proportion of people currently injecting reporting sharing needles/syringes decreased from 1999 to 2012, before increasing to 20% (288/1426) in 2019, with sharing of any injecting equipment at 37% (523/1429).

CONCLUSION
The HIV epidemic among people who inject drugs in EW&NI has remained relatively contained compared with in other countries, most likely because of the prompt implementation of an effective national harm reduction programme. However, risk behaviours and varied access to preventive interventions among people who inject drugs indicate the potential for HIV outbreaks.