We aimed to identify determinants of condom usage and unsafe sex in women having sex with a new partner. One hundred women attending either a genitourinary medicine (GUM) clinic or a family planning clinic participated in the study. Respondents were interviewed about last 3 new male partners, from the beginning of the sexual relationship through its development, if any. Data analysis was primarily qualitative, quantitative analysis was conducted where appropriate. Alternative contraceptive use was the most commonly reported determinant of condom usage overall. The most commonly reported determinant of condom use for prophylaxis was the woman's perception of her partner and the risks he presented. Models of risky sexual behaviour have focused on the individual's generalized estimation of risks of acquiring STDs. Existing models are poor predictors of risky sexual behaviour. We propose that it is the perceived risk presented by a particular individual partner, not global risk, which influences behaviour. An individual risk model is put forward.