This study presents a brief review of the historical and cultural context of polygamy in sub-Saharan Africa and examines the sociodemographic factors that influence polygamous union formation. Data were obtained from the Demographic and Health Surveys in Ghana (1988), Senegal (1986), Kenya (1989), and Zimbabwe (1988-89). The sample was restricted to currently married or cohabitating women. The proportion of women in a polygamous union was 48% in Senegal, 31% in Ghana, 23% in Kenya, and 16% in Zimbabwe. The authors state that rates may have been higher in Senegal and Ghana due to the higher involvement of women in the cultivation of root crops and trading at local markets. Rate differences indicated a greater proportion of men and women with no education and Muslim affiliation in the high polygamy countries of Senegal and Ghana in West Africa compared to Kenya and Zimbabwe. Single factor analysis was performed for the effects of women's formal education, men's formal education, religion, urbanization, current age, age at first marriage, and ethnicity. Multivariate analysis by country indicated the importance of rising husbands' education and the lack of significance of women's education. As husband's education rose to the secondary level, polygamy declined. Other significant factors were religion, ethnicity, and current age, which was the most important factor. In Ghana, the effect of husbands' education overwhelmed the effect of women's education. Current age was the most important explanatory factor, followed by religion. In Kenya, both women's and men's education, ethnicity, urbanization, and age were significant factors. Ethnicity was the most important factor. In Zimbabwe, every factor was significant. Women's education was the most important factor. Findings reveal different prevalence of polygamy and different effects of sociodemographic factors.