Anorexia nervosa (AN), a type of eating disorder, is a serious psychiatric illness that is characterized by an extreme loss of appetite. People with AN view themselves as overweight and cannot bring themselves to eat, even though most are dangerously thin. Signs of the disorder include unusual eating habits, such as avoiding food and meals, picking out a few foods and eating them in small quantities, or carefully weighing and portioning food. Some people with AN fully recover after a single episode, some have a fluctuating pattern of weight gain and relapse, and others experience a chronic course of illness over many years. Effective drugs to treat the disorder are lacking. In addition, most past research has examined the effect of medications during the initial phase of treatment, a time when AN patients may not respond to medication because of the acute effects of starvation. Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) that is commonly used to treat depression. This study will evaluate the effectiveness of fluoxetine versus placebo in reducing the rate of relapse of AN and enhancing the psychosocial and behavioral recovery of women who have already been treated for AN.