This paper develops a model where reductions in mortality are the main force behind economic development. The model generates a pattern of changes similar to the demographic transition, where gains in life expectancy at birth are followed by reductions in fertility and increases in the rate of human capital accumulation. The onset of the transition is characterized by a critical level of life expectancy at birth, which marks the movement of the economy from a Malthusian equilibrium to an equilibrium with investments in human capital and the possibility of long-run growth.