This study examines factors influencing HIV sero-status disclosure to sex partners among a sample of 630 HIV-infected men and women with recent sexual contact attending anti-retroviral therapy (ART) clinics in Cape Town, South Africa, with a focus on sex partner type, HIV-related stigma, and ART as potential correlates. About 20% of the sample had not disclosed their HIV status to their most recent sex partners. HIV disclosure to sex partner was more likely among participants who had a steady sex partner [Adjusted odds ratio (AOR) = 2.7; 95% CI: 1.6-4.6], had a partner with known-HIV status [AOR = 7.8; 95% CI: 3.2-18.7]; perceived less stigma [AOR = 1.9; 95% CI: 1.2-2.9]; and were on ART [AOR = 1.6; 95% CI: 1.1-2.3]. Stratified analyses by the type of sex partner further reveals that stigma and ART were significantly associated with HIV disclosure within steady relationships but were not significant correlates of HIV disclosure with casual sex partners. The findings support a positive prevention strategy that emphasizes increased access to ART, and behavioral interventions to reduce casual sex partnerships for persons who are HIV-positive. Mitigating the influence of HIV stigma on HIV status disclosure particularly within steady sex partnerships is also important and may be accomplished through individual and couple counseling.