The development of anorexia nervosa in a high-functioning, early adolescent, autistic female is described. This case raises the issue of co-occurrence of childhood-onset disorders sharing the phenomena of obsessions and compulsions. The role of dysregulation of the serotonergic neurotransmitter system as a common underlying mechanism in these disorders is suggested. Psychoactive agents affecting the serotonin system and in particular the atypical neuroleptic risperidone may be of value in these disorders. There is added benefit to the combined use of biological and behavioral therapies.