Feminist debate has moved away from an emphasis on how women differ from men and towards acknowledgement of differences among women. This article explores a division of growing importance for the new millennium: the division between women who choose to remain childless and those who choose to become mothers. The article demonstrates that more women are choosing to remain childless in the UK and the USA. It claims that the increase in childlessness is a demographic trend that is affecting the whole of the western, developed world. The main point of the article is to suggest that the way sex discrimination law is currently structured means that the demographic change identified will work to the disadvantage of both mothers and not-mothers.