Little is known about achievable levels of antiretroviral treatment (ART) adherence in resource-limited settings. We conducted a cross-sectional study of adherence among patients at Chris Hani Baragwanath Hospital's Adult HIV Clinic in Soweto, South Africa. Adherence was assessed using a 1-month, self-report questionnaire and was calculated as a ratio of doses taken to doses prescribed. The 66 patients studied had a mean age of 36.1 years, a median duration of ART use of 18 months, and an overall baseline median CD4(+) cell count of 200/mm(3) (IQR: 114-364). The adherence reported by these patients for the previous month was >95% for 58 patients (88%), 90-95% for 6 (9%) and, < 90% for 2 (3%). The main reasons given for missing doses were being away from home (30%), difficulty with the dosing schedules (23%), and running out of pills (12%). Adherence decreased considerably with fear of being stigmatized by the sexual partner (OR = 0.13 95%, CI 0.02-0.70). Plasma HIV RNA levels were <400 copies/ml in the majority of patients (73% of those with adherence >95% and 88% of patients with < or =95% adherence) and the overall median CD4(+) cell count rose to 324/mm(3) (IQR: 193-510). High adherence and viral suppression are achievable for a significant proportion of HIV-infected patients taking ART in a resource-limited area such as Soweto, South Africa. Strategies to maximize adherence in this setting should emphasize ready access to affordable and simple ART regimens, as well as HIV education programs to help increase awareness and decrease disease stigmatization.