Adherence to antiretroviral therapy (ART) is crucial for effective treatment, but can be quite complex. Non-adherence can adversely affect treatment outcomes. Although many studies have been done on adherence in the general population, few have included HIV-positive pregnant and postpartum women in resource-constrained settings. This review assessed the evidence on adherence among these groups of women. A systematic search of databases was completed between June and July 2011. Both qualitative and quantitative studies were included. Eighteen studies from a total of 6622 satisfied the inclusion criteria that included inter alia facilitators and barriers to adherence. This review highlighted that there is still no consensus on the definition and measurement of adherence; also multiple factors can affect a woman's ability to adhere to ART. Some of the barriers and facilitators identified were similar in both the type of study (qualitative and quantitative) and among the various countries. Findings indicated that the few studies in this population are conducted primarily in resource-rich settings. Such paucity of information warrants urgent attention; thus targeted research is needed to provide insight on adherence within this population.