Our aim was to investigate whether there is a season-of-birth effect in anorexia nervosa. In a meta-analysis, we compared the distribution of anorexia births (n = 1293) from four independent UK cohorts to that of the general UK population (n = 21 914 037), using both the Walter & Elwood seasonality and chi-squared tests. We found an excess of anorexia births from March to June (odds ratio (OR) = 1.15, 95% CI 1.03-1.29, P = 0.012) and a deficit from September to October (OR = 0.8, 95% CI 0.68-0.94, P = 0.007). These results indicate that environmental risk factor(s) are operative during gestation or immediately after birth and their identification will be important for disease prevention strategies.