["American Journal of Human Biology, Volume 38, Issue 7, July 2026. ", "\nABSTRACT\n\nBackground\nResearch across different global contexts has begun to highlight the potential negative consequences of polygynous marriage, especially for women and children. However, there is a knowledge gap about how polygynous family structures may impact child health outcomes in Afghanistan, where polygynous marriage is highly prevalent. Therefore, this study investigates the effects of polygyny on key health outcomes among children under 5 years of age in Afghanistan.\n\n\nMethods\nIn this cross‐sectional study, we used secondary data from the Afghanistan Multiple Indicator Cluster Survey (MICS) 2022–2023. A weighted sample of 30 751 children was included in the analysis. Key child health outcomes examined in the current study included malnutrition, immunization coverage, developmental status, and child morbidity and mortality. We applied multivariable Poisson regression models to assess the effect of polygyny on these outcomes.\n\n\nResults\nOf the 30 751 children in the sample, 2264 (7.4%) belonged to polygynous households. Children belonging to polygynous households had an increased risk of diarrhea (adjusted prevalence ratio [APR] 1.11, 95% CI: 1.02–1.21), fever (APR 1.07, 95% CI: 1.01–1.14), wasting (APR 1.45, 95% CI: 1.11–1.91), and child mortality (APR 1.36, 95% CI: 1.18–1.56). Additionally, household wealth improves some (immunization coverage and developmental status), but not all of the risks associated with polygyny.\n\n\nConclusion\nPolygyny was associated with an increased risk of specific adverse child health outcomes, including diarrhea, fever, wasting, and child mortality. While household wealth mitigated some disadvantages, it did not fully offset the health risks associated with polygyny. These findings may enable a better understanding of the effects of polygynous marriages on child health outcomes in Afghan society and provide evidence for future policy efforts and interventions.\n\n"]