PURPOSE OF REVIEW: This review provides an update of recent data on the development of HIV-1 drug resistance during treatment and its transmission in sub-Saharan Africa after the scale-up of antiretroviral therapy (ART). RECENT FINDINGS: Evidence is accumulating of a rising prevalence of transmitted HIV drug resistance (TDR), predominantly associated with nonnucleoside reverse transcriptase inhibitors (NNRTIs), in east and southern Africa. Pretherapy resistance is associated with first-line therapy failure. Accumulation of resistance mutations during first-line failure can be prevented by early detection and timely switching to second-line ART. Important gaps in service delivery and programme performance, associated with resistance development, affect a considerable proportion of ART programmes, particularly with respect to inadequate supply systems and patient retention. The reduction in new HIV infections associated with earlier use of ART is predicted to outweigh the risk of increasing TDR. Future levels of TDR are estimated to be diminished by improving switching practices to second-line regimens. SUMMARY: TDR is on the rise after the recent scale-up of ART in Africa. To prevent the development and spread of drug resistance and sustain the effectiveness of ART programmes, there is a need to improve drug supply systems, patient retention and access to routine viral load monitoring. Enhanced resistance monitoring is warranted in Africa.