Based on data extrapolated from over 1000 sexual diaries and interpreted by Project SIGMA (Socio-sexual Investigations of Gay Men and AIDS), this work portrays the reality of gay sex and aims to understand it in relation to the transmission of HIV. By basing its findings on diaries, the work ensures the participation of marginalized groups, such as SM practitioners, married men, under-age men, men in the armed forces and men who have casual sex. Among the issues examined are genitalia and body image, types of gay men, varieties of sexual practice, sexual role and orgasm, and what happens in a sexual session.