This study examines whether the mental and physical health of single mothers benefit from marriage or cohabitation compared to childless women who marry. Results indicate that marrying is associated with similar declines in psychological distress for single mothers and childless women, but only when that marriage endures. Single mothers do not receive the same physical health benefits from entering an enduring marriage, in part because single mothers have lower levels of marital quality. Entering and exiting marriage is worse for the mental and physical health of single mothers than for other women and in some cases, worse than remaining unpartnered. Enduring cohabiting unions offer few psychological or physical health benefits to either group but short-lived cohabiting unions are associated with increased distress. (Contains 4 tables and 5 notes.)