Beta-galactosidase (lactase) allows the digestion of lactose as its component sugars, galactose and glucose. Considerable variation exists worldwide in the prevalence of adults who lose the ability to digest lactose after infancy (hypolactasia) as well as in the amount of milk products they consume. Clearly, those populations in which hypolactasia is infrequent and milk consumption high will have greater dietary exposure to galactose. Because there is clinical and experimental evidence that galactose may be toxic to ovarian germ cells, the authors sought to determine whether age-specific fertility rates in various countries correlate with the prevalence of adult hypolactasia and per capita milk consumption by analysis of published data on these variables. The authors found significant correlations among these variables such that fertility at older ages is lower and the decline in fertility with aging is steeper in populations with high per capita consumption of milk and greater ability to digest its lactose component. These demographic data add to existing evidence that dietary galactose may deleteriously affect ovarian function.