Understanding the financial well-being of single mothers who care for children with developmental disabilities is important to ensure that public policies can be effectively targeted to support these vulnerable families. The authors analyze data from the Survey of Income and Program Participation to describe income poverty, asset poverty, income, net worth, and liquid assets of U.S. single, working-age mothers (n = 242) of children and adult children with developmental disabilities. The well-being of these mothers was compared to the situation of married mothers of children with developmental disabilities (n = 345) and of single mothers who did not have children with developmental disabilities (n = 6,547). Compared with both married mothers of children with developmental disabilities and single mothers without children with developmental disabilities, single mothers of children with developmental disabilities had markedly worse financial well-being across a range of income- and asset-based measures. Single mothers caring for children with developmental disabilities face adverse financial well-being as compared with other mothers. Policy makers should consider targeted measures to improve the financial well-being of these parents.