To determine rates of survival, viral suppression, and immunologic change after 1 year on second-line antiretroviral therapy, we conducted a cohort study among 328 patients initiated on zidovudine, didanosine, and lopinavir/ritonavir. All patients who switched to standard second-line therapy at a large urban public-sector clinic in Johannesburg, South Africa, were included. A year after initiating second-line therapy 243/313 [78%; 95% confidence interval (CI) 73%-82%], subjects were alive and in care. Further, 203/262 (77%; 95% CI: 72%-82%) had a suppressed viral load by 1 year. Mean CD4 gain by 12 months was 133 cells/μL (95% CI: 106-160). Patients on second-line therapy had a small decreased likelihood of being alive and in care by 1 year [hazard ratio (HR) 0.84; 95% CI: 0.73-0.97] as time-matched comparisons on first-line antiretroviral therapy (ART). Patients switched before 2 viral loads >1000 (HR 1.68; 95% CI: 1.08-2.61), and those switched for reasons not related to noncompliance with first-line (HR 1.83; 95% CI: 1.14-2.93) were more likely to achieve virologic suppression by 1 year on second-line ART. As rates of treatment failure over the first year on second-line therapy were low, provision of second-line treatment to patients who fail their first-line ART should be considered a high priority in resource-poor settings.