Over 1200 women, drawn from London's two specialist sexual health clinics and lesbian and bisexual community groups, were surveyed between 1992 and 1995 about their sexual histories and behaviour.
The results, published in the journal Sexually Transmitted Infections, showed that 85% of the women had a history of sex with men. For 12% this had been within the past year, but for seven out of 10, this had been 4 or more years earlier.
The first sexual experience tended to be with a man, at an average age of 18, progressing to first sex with a woman three years later, on average. One in four lesbians and almost a third (29%) of bisexual women had been pregnant.
Those under 30 were almost twice as likely to describe themselves as bisexual as women over 30. In all, 101 women described themselves in this way.
The average number of sexual partners in the preceding year was one, the survey showed.
Among the 328 women asked about safer sex practices, a third who had had penetrative sex with men had never used a condom. And over 85% of lesbians engaging in oral sex with other women did not use dental dams, while one in five of those sharing sex toys said they did not wash them before sharing.
The authors point out that research shows that, although uncommon, women can pass on sexually transmitted infections to other women, including herpes, trichomoniasis, papilloma virus, syphilis, HIV and bacterial vaginosis.
The authors note that the demand for specialist lesbian and bisexual health services in London and other UK cities indicates that mainstream services are failing to meet the needs of these groups.
It is easy for doctors and other health professionals to make assumptions about lesbian and bisexual women's sexual behaviour, and ignore the health issues that might arise from varied sexual practices with both men and women, they say.