Objectives: Internalised homonegativity (IH) is hypothesised to be associated with HIV risk behaviour and HIV testing in men who have sex with men (MSM). We sought to determine the social and individual variables associated with IH and the associations between IH and HIV-related behaviours. Design and setting: We examined IH and its predictors as part of a larger Internet-delivered, crosssectional study on HIV and health in MSM in 38 European countries. Participants: 181 495 MSM, IH data analysis subsample 144 177. All participants were male, over the age of consent for homosexual activity in their country of domicile, and have had at least one homosexual contact in the past 6 months. Methodology: An anonymous Internet-based questionnaire was disseminated in 25 languages through MSM social media, websites and organisations and responses saved to a UK-based server. IH was measured using a standardised, cross-culturally appropriate scale. Results: Three clusters of European countries based on the level of experienced discrimination emerged. IH was predicted by country LGB (lesbian, gay and bisexual) legal climate, Gini coefficient and size of place of settlement. Lower IH was associated with degree the respondent was 'out' as gay to others and older age. 'Outness' was associated with ever having an HIV test and age, education and number of gay friends, while IH (controlling for the number of nonsteady unprotected sex partners and perceived lack of control over safe sex) was associated with condom use for anal intercourse. Conclusions: IH is associated with LGB legal climate, economic development indices and urbanisation. It is also associated with 'outness' and with HIV risk and preventive behaviours including HIV testing, perceived control over sexual risk and condom use.