BACKGROUND: We examined attendance at sexually transmitted disease (STD) clinics and the prevalence, distribution, and associated demographic and behavioral factors of self-reported sexually transmitted infections (STIs) in a population survey of sexual attitudes and lifestyles. METHODS: We analyzed data from stratified probability sample surveys obtained through the British National Surveys of Sexual Attitudes and Lifestyles (Natsal), which was undertaken in 1990 (n=13,765) and 2000 (n=11,161) among men and women aged 16-44 years. National STD surveillance data for 1999 were used to determine disease- and risk factor-specific proportionate population burden (PPB). RESULTS: Between 1990 and 2000, the number of subjects who reported having attended an STD clinic during the past 5 years increased from 4.3% to 7.6% among men and from 3.3% to 6.6% among women. In 2000, 3.0% of men and 4.0% of women reported having received a diagnosis of an STI during the past 5 years; 77.6% of men and 60.3% of women with an STI had attended an STD clinic. Reported STI acquisition was independently associated with age, increasing numbers of sex partners, male homosexual partners, and partners from abroad (for women only). Of all reported STIs during the past 5 years (PPB, 10.2%), 10.2% were reported by the 2.9% of men who reported having had homosexual partners during the past 5 years. Of all reported STIs in the past 5 years (PPB, 41.6%), 41.6% were reported by the 4.0% of women who reported having > or =10 sex partners during that time. Analysis of national STI surveillance data showed that the PPB for new episodes of Chlamydia trachomatis diagnosed among homosexual men was 2.8%, that for gonorrhea was 17.4%, and that for syphilis was 32.1%. CONCLUSIONS: Numbers and types of sexual partnerships remain the dominant individual and population risk factors for STI acquisition. Combined population behavior and surveillance data demonstrate the high PPB for STIs attributable to key risk factors. PPB may be a useful indicator of epidemic "phase" and may help target resources and guide prevention strategies.