BACKGROUND: Over the past 20 years, there has been a huge increase in the number of overseas trips made by UK residents. Although a number of studies have examined the frequency of overseas partner acquisition, they have used convenience samples and thus are not generalisable to the British general population. METHODS: A national probability sample survey was carried out in 1999-2001 of 12,110 men and women aged 16-44 years resident in Britain. Sociodemographic, health-related, travel, sexual behaviour and attitudinal data were collected by computer-assisted interviewing. The main outcomes were the proportion of British residents who reported new sexual partners overseas in the past 5 years, the country of origin of these new sex partners, and the association between reporting a new partner while overseas with a range of demographic, behavioural and attitudinal variables. RESULTS: 13.9% of men and 7.1% of women reported having new sexual partner(s) while overseas in the past 5 years. Among respondents who were aged 16-24 and never married, the proportions were significantly higher (23.0% of men and 17.0% of women). Half of those with new sex partners overseas reported their partner's origin as the UK, and over a third as another European country. In addition to age and marital status, reporting new partners overseas was associated with a higher number of partners, paying for sex (among men), reporting a diagnosis of sexually transmitted infection, and HIV testing. Adjustment for sociodemographic factors attenuated the magnitude of, but did not remove, these associations. CONCLUSIONS: A substantial minority of young, unmarried people form new sexual partnerships abroad, but these are typically with residents from the UK or other European countries. Those who have new partners abroad are likely to have higher-risk sexual lifestyles more generally, and to be at higher risk of sexually transmitted infections. Greater attention should be paid to sexual health promotion for travellers abroad, especially young travellers, emphasising the risks of new sexual relationships with compatriots as well as those from other countries in terms of STI/HIV acquisition and onwards transmission.