Inconsistent condom use among persons on antiretroviral treatment (ART) is a major public health concern because of the risk of HIV transmission. This study examined the association between socio-demographic variables and knowing partners' HIV status, multiple sex partners, and consistent condom use among 400 HIV-infected adults who had received ART for at least six months in Johannesburg, South Africa. The study used a cross-sectional survey and a structured interviewer administered questionnaire. Over half (n = 225, 56.3%) of participants were on ART for more than two years. Two thirds (n = 234, 63.2%) were aware of partner's HIV status. Over a third (n = 136, 34.0%) reported having more than one sex partners.