This cross-sectional study analyses determinants of condom-use behaviour among patients attending dedicated STD clinics in South Africa. A structured interviewer-administered survey was conducted among 1473 patients. Patients' beliefs and attitudes towards condom use in general, as well as their personal condom-use behaviour were measured. Their perceptions, regarding the social influence of their partners and friends on their condom use, and of their self-efficacy in using condoms, while infected with an STD were also measured. Condom use, as a dependent variable, was examined and patients were placed in a pre-contemplation stage if they had never used a condom, contemplation if they had seriously thought of using a condom, some action stage if they sometimes used a condom and regular action stage if they used a condom every time. The relationships between the stages of change, as dependent variables, and the independent variables were investigated for both those patients with steady partners and those with outside partners. This was performed by stepwise multiple regression analyses. The variables that significantly explained stages of change were similar for patients with steady partners and those with outside partners. In both partner groups communication was the variable most strongly associated with the use of condoms. General self-efficacy in condom use, self-efficacy in condom use with a partner and attitudes towards the use of condoms played a role in determining patients' different stages of change.