BACKGROUND:Evidence to understand which gay and bisexual men (GBM) inject drugs remains scant, especially in the UK. We describe correlates of last-year injecting in UK GBM, and characterise subgroups of GBM who inject drugs by types of drugs used. METHODS:Using data from the 2014 Gay Men's Sex Survey, an opportunistic internet-based survey conducted of GBM living in the UK, we examined via logistic regression correlates with any injecting of six drugs (amphetamine/speed, crystal methamphetamine, heroin, mephedrone, GHB/GBL, and ketamine) in the last year. We estimated latent class models to understand underlying subgroups of injecting drug use among GBM reporting injecting drug use in the last year. RESULTS:Injecting was most common in GBM who were of middle age, who were HIV seropositive, and who lived in London, and was significantly associated with sexual risk with multiple partners in the last year, whether steady or non-steady. Most GBM who engaged in injecting either injected crystal methamphetamine, mephedrone or both (class 1, chemsex, 88.6% of injectors), whereas a smaller group had a focus on opiates (class 2, opiate, 7.9%). A small but identifiable subgroup (class 3, eclectic, 3.5%) engaged in injecting across the range of drugs examined. CONCLUSIONS:This is the first epidemiological analysis to describe subgroups of injecting, and to describe correlates of injecting drug use, in UK GBM. Implications for design of harm reduction services include a need to focus on injecting drug use beyond opiates, currently the focus of most harm reduction services.