Our aim was to investigate whether there is a season-of-birth effect inanorexia nervosa. In a meta-analysis, we compared the distribution ofanorexia births (n = 1293) from four independent UK cohortsto that of the general UK population (n = 21 914 037),using both the Walter & Elwood seasonality and chi-squared tests. Wefound 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 fromSeptember to October (OR = 0.8, 95% CI 0.68–0.94, P =0.007). These results indicate that environmental risk factor(s) areoperative during gestation or immediately after birth and theiridentification will be important for disease prevention strategies.