BackgroundMembership in diverse racial, ethnic, and cultural groups is often associated with inequitable health and mental health outcomes for diverse populations. Yet, little is known about how cultural adaptations of standard services affect health and mental health outcomes for service recipients. This systematic review identified extant themes in the research regarding cultural adaptations across a broad range of health and mental health services and synthesized the most rigorous experimental research available to isolate and evaluate potential efficacy gains of cultural adaptations to service delivery.MethodsMEDLINE, PsycINFO, CINAHL, EMBASE, and grey literature sources were searched for English-language studies published between January 1955 and January 2015. Cultural adaptations to any aspect of a service delivery were considered. Outcomes of interest included changes in service provider behavior or changes in the behavioral, medical, or self-reported experience of recipients.ResultsThirty-one studies met the inclusion criteria. The most frequently tested adaptation occurred in preventive services and consisted of modifying the content of materials or services delivered. None of the included studies focused on making changes in the provider’s behavior. Many different populations were studied but most research was concerned with the experiences and outcomes of African Americans. Seventeen of the 31 retained studies observed at least one significant effect in favor of a culturally adapted service. However there were also findings that favored the control group or showed no difference. Researchers did not find consistent evidence supporting implementation of any specific type of adaptation nor increased efficacy with any particular cultural group.ConclusionsConceptual frameworks to classify cultural adaptations and their resultant health/mental health outcomes were developed and applied in a variety of ways. This review synthesizes the most rigorous research in the field and identifies implications for policy, practice, and research, including individualization, cost considerations, and patient or client satisfaction, among others.Electronic supplementary materialThe online version of this article (doi:10.1186/s12913-016-1953-x) contains supplementary material, which is available to authorized users.