DSM-IV Diagnostic Criteria
1. Refusal to maintain body weight at or above a minimally normal weight for age and height (e.g., weight loss leading to maintenance of body weight less 85% of that expected; or failure to make expected weight gain during a period or growth, leading to body weight less than 85% of that expected.
2. Intense fear of gaining weight or becoming fat, even though underweight.
3. Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight.
4. In postmenarchial females, the absence of at least three consecutive menstrual cycles.