The article explores a series of questions and hypotheses related to polygynous family structures and both household and individual-level food security outcomes, using the World Bank Living Standards Measurement Survey data from Nigeria, collected in 2011 and 2013. A Correlated Random Effects (CRE) model is used to examine the relationship between polygyny and household-level food security, and the degree to which it is mediated by household wealth, size, and livelihood. A Household Fixed Effect model is employed to explore whether a mother’s status as monogamous versus polygynous relates systematically to her child’s health, and also whether child outcomes of senior wives are better than outcomes of junior wives within polygynous households. We find that polygynous households have better food security outcomes than monogamous households with differences in household composition and agricultural livelihood as potential explanatory mechanisms. We also find that within polygynous households, children of junior wives have better health outcomes than children of senior wives.