Prepubertal anorexia nervosa and gender identity disorder of childhood, both rare conditions, are described. The aetiology of both conditions is discussed and the relevance of psychosexual problems to eating disorders is explored. A case is reported of a 12-year-old boy with both conditions where there was a clear aetiological precipitant for the onset of anorexia. His assessment, treatment, response and prognosis are described. The ethical conditions relating to treatment of gender identity disorder of childhood are discussed.