Using published data, largely from the 1970s, the author compared ovarian cancer incidence, per capita milk consumption, and population estimates of lactase persistence (the ability to digest lactose after infancy) in 27 countries. Significant positive correlations were noted between ovarian cancer incidence, per capita milk consumption, and lactase persistence. Lactase persistence showed a stronger association than milk consumption or animal fat consumption in multiple regression models. The author speculates that toxicity from the lactose component of milk and, more specifically, galactose, the digestion of which is facilitated by lactase persistence, may provide a biologic basis for the correlation.