Background: Researchers from a variety of disciplines have presented data indicating that polygynous marriage is damaging to child health. This work has been used to support the classification of polygyny as a 'harmful cultural practice' and to advocate for marital reform across sub-Saharan Africa. Objective: We present a critical review of studies of polygyny and child health, highlighting issues of context and variation. We also consider methodological limitations of the existing literature. Methods: We describe key features of African polygyny, variation in its form, and the pathways through which polygyny has been hypothesized to influence child health. We then review the available empirical evidence, focusing on cross-national studies utilizing the Demographic and Health Surveys and relatively small-scale studies based on more specific socioecological settings (e.g., among particular ethnic groups). Conclusions: We conclude that (i) heterogeneity in the impact of polygyny on child health should be anticipated a priori given substantial variety in its form, locally available alternatives, and the wider context of the practice; (ii) available evidence suggests that polygyny is most frequently associated with poor child health, but there are also instances where polygyny appears inconsequential or even beneficial to children; and (iii) methodological shortcomings are rife across the literature, severely undermining our ability to make causal inferences from observed relationships between polygyny and child health. Contribution: Theoretical and empirical considerations imply that a singular health consequence of polygyny does not apply across all ecological and cultural settings. We encourage a more nuanced stance on polygyny in future academic and policy discourse.