Pattern of Birth in Anorexia Nervosa I: Early-Onset Cases in the United Kingdom Beth Watkins, 1  Kate Willoughby, 1 Glenn Waller, 1 Lucy Serpell, 1,2 and Bryan Lask 1,2 1 Department of General Psychiatry, St. George's Hospital Medical School, University of London, United Kingdom 2 Eating Disorders Service, Huntercombe Manor Hospital, Maidenhead, Berkshire United Kingdom Accepted 19 September 2001 Abstract: Objectives: Previous studies suggest that adults with anorexia nervosa are more likely to be born in spring and early summer. This study examines whether this pattern of birth is true of early-onset anorexia nervosa, and whether there is a relationship between environmental temperature at assumed time of conception and a later diagnosis of anorexia nervosa. Method: The population were children and adolescents with diagnoses of anorexia nervosa (N  259) or ``other eating disorders'' (N  149). Distribution of births across the year was compared between groups and relative to standard population norms. Temperature at assumed time of conception was taken from meteorological records. Results: There was a signi®cant preponderance of births among those with anorexia nervosa between April and June, compared with the other months of the year and with the ``other eating disorders'' group. Anorexia nervosa was also associated with higher environmental temperature at assumed time of conception. Conclusions: Among early-onset cases in the United Kingdom, patients with anorexia nervosa are more likely to be born between April and June, and to be conceived during warmer months. A tentative ``temperature at conception'' hypothesis is advanced to explain these ®ndings and to generate further research. Ó 2002 by Wiley Periodicals, Inc. Int J Eat Disord 32: 1117, 2002. Key words: pattern of birth; anorexia nervosa; season of birth; children; eating disorders; risk factors INTRODUCTION A season of birth tendency has been well documented in schizophrenic and affective disorders, with a bias toward winter/spring births (e.g., Torrey, Miller, Rawlings, &  Correspondence to: Beth Watkins, Child and Adolescent Eating Disorders Research Team, Department of General Psychiatry, St. George's Hospital Medical School, Jenner Wing, Cranmer Terrace, London, SW17 0RE, United Kingdom. E-mail: e.watkins@sghms.ac.uk Grant sponsor: The Gordon Carlton Memorial Fund. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/eat.10057 Ó 2002 by Wiley Periodicals, Inc.