The link between degree of urbanisation and a number of mental disorders is well established. Schizophrenia, psychosis and depression are known to occur more frequently in urban areas. In our primary care-based study of eating disorders, the incidence of bulimia nervosa showed a dose-response relation with degree of urbanisation and was five times higher in cities than in rural areas. Remarkably, anorexia nervosa showed no association with urbanisation. We conclude that urban life is a potential environmental risk factor for bulimia nervosa but not for anorexia nervosa. These findings provide a promising avenue for further research into the aetiology of eating disorders.