In a National study of gay men’s sexual behaviour in the context of HIV transmission, a schema was evolved for encoding and reporting the structure of sexual activity: the Sexual Behaviour Code (SBC). It has linguistic properties, is easily learned and employed, and generalizes easily to heterosexual behaviour. Each sexual session (sentence) comprises a sequence of sexual acts (words), which in turn consists of a sexual behaviour (root), the modality (prefix), and the outcome/ ejaculation (suffix). Other aspects (partner/s, drugs, condoms) are encoded as precedents and accompaniments of the acts. The SBC is also used to define a comparable and flexible research instrument for eliciting systematic information on sexual behaviour: the Inventory of Sexual Behaviour (ISB), now used in all WHO/ GPA studies of homosexual response. Issues of validity and reliability are addressed, and forms of analysis of the resulting data are discussed for sexual diaries and inventories.
