Several sites of adult neurogenesis in the brain are well established, and recent studies have suggested that there may also be a neurogenic niche in the hypothalamus. Here, the authors show that radial-glia-like cells known as tanycytes in the median eminence of the hypothalamus proliferate and generate new neurons in adult mice. The rate of neurogenesis was altered by changes in diet (a high-fat diet induced more neurogenesis), and inhibiting hypothalamic neurogenesis reduced weight gain, suggesting a role for this process in weight regulation.