The scale-up of antiretroviral therapy in sub-Saharan Africa has significantly reduced mortality from AIDS. Hamers et al. explores the impact of pretreatment HIV-1 drug resistance on virologic failure, immunologic response, and acquisition of drug resistance after 1 year of first-line antiretroviral therapy by longitudinally evaluating 2579 participants with pretreatment drug resistance results from the PharmAccess African Studies to Evaluate Resistance Monitoring (PASER-M) cohort. Participants with pretreatment drug resistance who were given a treatment regimen with reduced activity to at least one prescribed drug had a significantly greater risk of virologic failure and acquired drug resistance compared with both participants without pretreatment drug resistance, and participants with pretreatment drug resistance who were prescribed fully active regimens. This paper by Hamers et al. validates the need for at least three fully active antiretroviral drugs to prevent the acquisition of drug resistance and to optimize treatment success in resource limited settings.