Familial relationships are popularly and sociologically viewed as crucial to the social support of elderly people, and of these the relationships between adult children and their parents are generally regarded as the most important (Finch and Mason 1993). But could these expectations be part of a cultural myth? In actuality, does the distinction between parenthood and childlessness make much difference to social support in old age? The present paper addresses this question. Using data from Liverpool, it compares the support networks of older people in three categories: parents (nearly always married); those who married but remained childless; and those who did not marry and remained childless. Its principal finding is that childlessness has a negative impact on support network strength only for single men and for married women. This suggests that youthful investment in a lasting marriage incurs high social opportunity costs for women in old age, unless offset by the survival of children. The findings have implications for the evaluation of social policies that are based on the expectation that individual female family members, in the context of a male-breadwinner family, will provide ‘caring’ for dependent persons. Such provision of care may incur diminished receipt of care for some women in old age.