ObjectiveTo examine the association between seeking sex on the Internet and sexual risk behaviour among gay men in London.MethodsIn January–February 2000, gay men in London gyms were asked to complete self-administered questionnaires concerning use of the Internet, history of sexually transmitted diseases (STD) and recent unprotected anal intercourse (UAI). Internet sex seekers were compared with other men, also with Internet access, who did not seek sex in this way.ResultsOf 743 gay men included in the analysis (121 HIV-positive, 465 HIV-negative, 157 never-tested), 80.9% (601) had access to the Internet. Among those who had access, 34.4% (207) had used the Internet to find a sexual partner; this did not vary significantly by HIV status (P= 0.3). Internet sex seekers were more likely to have had an STD (HIV-negative men, 26.9 versus 17.5%,P= 0.04) or gonorrhoea (HIV-positive men, 22.2 versus 5.8%,P= 0.04) in the previous year than other men with Internet access. HIV-negative Internet sex seekers were also more likely to report non-concordant UAI in the previous 3 months [23.1 versus 11.8%; adjusted odds ratio (aOR), 1.9; 95% confidence interval (CI), 1.2–3.5;P= 0.01]. HIV-positive Internet sex seekers were more likely to report UAI with another positive man (37.8 versus 7.4%; aOR, 7.9; 95% CI, 1.8–34.6;P= 0.006).ConclusionSeeking sex on the Internet was associated with recent STD and high-risk sexual behaviour among HIV-positive and -negative gay men in London. The contribution of seeking sex on the Internet to the recent increase in high-risk behaviour among London gay men merits further investigation.