Women's social networks and social power are increasingly seen as important factors modulating their health in sub-Saharan Africa. Polygyny, a common marital structure in many societies, mediates important intra-household relationships by requiring both competition and co-operation among co-wives. Using mixed methods, semi-structured questionnaires were administered to 298 women aged 15-84 living in the Kolondiéba region of rural Mali in 1999, and supplemented by detailed interviews with 40 women. Three categories of outcome were explored: illness experience, therapeutic itinerary and social support received. Quantitative data were analysed using regression analysis and qualitative data using a grounded theory approach. In quantitative analyses, controlling for age and household wealth index, senior wives were less likely to be escorted to a healer by their husbands during illness than were junior wives or monogamous women. Polygynous women were also less likely to obtain a treatment for which there was a monetary fee. Fewer than one-third of polygynous women reported the assistance of a co-wife during illness in any given task. In qualitative analyses, women further related varied mechanisms through which polygyny impacted their health trajectories. These ranged from strongly supportive relationships, to jealousy because of unequal health or fertility, bias in emotional and material support provided by husbands, and accusations of wrong-doing and witchcraft. This study highlights the need for more prospective mixed methods analyses to further clarify the impact of polygyny on women's health-related experiences and behaviours in sub-Saharan Africa.