AbstractHIV+ South African women who achieved viral suppression during routine antenatal care, but later experienced a viremic episode (viral load >1000 copies/mL), were examined for presence of antiretrovirals and classified as “nonadherers” or “suboptimal adherers.” Women were tested for drug resistance mutations (DRMs) at several time points and underwent viral load testing 36–60 months postpartum. Suboptimal adherers were more likely to have DRM detected during their viremic episode (P = .03) and at a subsequent viremic time point (P = .05). There was no difference in levels of viral suppression 36–60 months later in women with DRM detected vs women who had no evidence of DRM (P = .5).