BMC Public Health 2006, 6:127 http://www.biomedcentral.com/1471-2458/6/127 men and women and between people classified as gay, lesbian and bisexual would make it difficult to generalise our finding to either sex or people classified as gay, lesbian or bisexual as a whole. Recruiting general practice attend- ees also means that the prevalence of physical or psycho- logical difficulties may have been higher than in the general population, given that participants would often have been seeking help for medical or social problems. Our results are hence limited to the people recruited to our study and may not represent that of the UK or Europe as a whole. We used a definition of sexuality based on criteria devel- oped for this study. There is little consensus on how to measure sexual orientation. Several issues should be con- sidered. Firstly, sexual responsiveness to others of the same sex, like most human traits is believed to be contin- uously distributed in the population [17,33]. Secondly, it may be incorrect to presume that such traits are stable within each person over time [34]. Thirdly, conflating any same-sex experiences with a categorization of the person as homosexual may present limitations when defining sexuality. Lastly, defining sexuality solely on the basis of sexual experience [17] may exclude people who fantasize about sex with others of the same sex but never have sex- ual contact [35]. Modern concepts of sexual orientation consider personal identification, sexual behaviour and sexual fantasy [36]. Few studies, however, utilise all these three definitions in arriving at a composite categorization of sexuality. One widely established definition is a person "with an orientation towards people of the same gender in sexual behaviour, affection, or attraction, and/or self- identity as gay/lesbian or bisexual" [37]. Using these types of definition, there is evidence that at least five per cent of people in western countries are gay or bisexual [14,34- 38]. In our study classification of sexuality was limited by the Kinsey classification for which no time frame was applied. Moreover the classification of gay, bisexual and heterosexual as applied to people recruited in our study has not been previously used in similar population and it is possible that a different classification using the Kinsey scale might have yielded different results. Nevertheless, based on the categorization of sexual orientation used in this study, prevalence estimates of gay, lesbian and bisex- ual people in our sample closely matched that reported from London in a larger UK wide population survey [14]. There were also limitations in the way some data were col- lected. We assessed sexual behaviour using standardised questionnaires that were not explicit in their definition of sexual intercourse [27-29]. Many people (gay or straight) regard sexual intercourse differently and do not always realise that it means penetrative (vaginal or anal) sex. Fur- thermore, for gay men receptive anal intercourse can be regarded as "sexual intercourse" more often than insertive anal intercourse. At first sight our figures for sexual inter- course in gay classified men may seem low and those for lesbian classified woman high. However, most of our evi- dence on the prevalence of anal intercourse in gay men arises from particular populations, such as younger age groups, men attending clubs and bars or those living in gay neighbourhoods. Studies using diary records show that reported rates of intercourse depend on whether not the man has a regular same-sex partner and if so whether the relationship is open or closed. Those in closed rela- tionships and those without regular partners may have relatively low rates of penile-anal intercourse [39]. Given the wide age range in our sample and the fact that these men were not selected on any sexual risk grounds, it is not surprising that only 35% of gay men reported sexual inter- course in the preceding 4 weeks. Moreover, vaginal pene- trative practices using sex toys and fingers or hands are commonly reported by lesbian and bisexual women [40,41]. Mental health of gay men and lesbians Our finding of higher rates of common psychological symptoms of depression and anxiety, in gay classified men accords with those of a recent study of the mental health of gay men and lesbians in England and Wales in which a large sample was recruited by snowball sampling [12]. There are a number of reasons why gay people may be more likely to report psychological difficulties, which include difficulties growing up in a world orientated to heterosexual norms and values and the negative influence of social stigma against homosexuality. In addition, the gay commercial world in which some men and women may participate to find partners and friends may make misuse of alcohol and cigarettes more likely [3,12]. The former in particular can have adverse effects on mental well-being. Finally, our results add to evidence that sexual experiences in childhood in men classified as gay or bisex- ual may play a role in adult psychological adjustment [42,43]. Why this is not the case in lesbian and bisexual classified women requires further exploration. Mental health of bisexual people Much less is known about how bisexual, as opposed to gay people, accept their sexual orientation or whether the possibility of having partners of either sex introduces dif- ficulties. Although there is anecdotal evidence that bisex- uality is regarded negatively by gay and lesbian political and social groups, it may present to people living in a pre- dominantly heterosexual world as being of a more accept- able social status than that of a gay or lesbian identity. We found, however, little difference in psychological distress between people classified as bisexual and heterosexual, despite the finding that women classified as bisexual reported more sexual experiences in childhood than het- erosexual classified women. This finding has also been Page 7 of 12 (page number not for citation purposes)