Polygyny has shown a positive association with intimate partner violence (IPV), yet the nature and mechanisms of this association are not well understood. This study uses data from rural Mozambique to distinguish women in polygynous unions by rank and co-residence. Findings show that senior wives report higher rates of violence than their junior-wife and monogamously married counterparts. At the same time, no difference is detected between junior wives and women in monogamous marriages. Additionally, the analysis finds that polygynously married women living away from their co-wives report higher rates of violence than both women co-residing with co-wives and women in monogamous unions, while the difference between the latter two categories is not statistically significant. However, the results also indicate that senior wives living away from their co-wives face particularly high risks of violence. These findings illustrate the social complexity of polygynous marriages and resulting differential vulnerabilities of women in them.