We analyse the economic consequences for poor countries of investing in female health within a unified growth model featuring health-related gender differences in productivity. Better female health accelerates the demographic transition and thereby the take-off towards sustained economic growth. By contrast, male health improvements delay the transition and take-off because they tend to raise fertility. However, households tend to prefer male health improvements over female health improvements because they imply a larger static utility gain. This highlights the existence of a dynamic trade-off between the short-run interests of households and long-run development goals.