Background Since May 2004, 10 central and east European (CEE) countries have joined the European Union. While HIV rates remain low among men who have sex with men (MSM) in CEE countries, there is no research on the sexual behaviour of CEE MSM in the UK. Methods CEE MSM living in the UK (n=691) were recruited for an online questionnaire by two popular MSM websites. Results The majority of men had arrived in the UK since May 2004. A previous sexually transmitted infection (STI) diagnosis was reported by 30.7%, and 4.8% reported being HIV positive, the majority diagnosed in the UK. Unprotected anal intercourse with a casual partner of unknown or discordant HIV status was reported by 22.8%. Men who had been in the UK for longer (>5 years vs 10 partners, pConclusion CEE MSM in the UK are at risk for the acquisition and transmission of STI and HIV through unprotected anal intercourse with non-concordant casual partners. Sexual mixing with men from other countries, commercial sex and increased partner numbers may introduce additional risk. This has important implications for the cross-border transmission of infections between the UK and CEE countries.