Although amenorrhea is no longer a specific criterion required to make the diagnosis of anorexia nervosa (AN), the relationship between restrictive eating and menstrual status remains important in the diagnosis, treatment, and consequences for patients with eating disorders. Clinicians should understand the relationship between menstrual irregularities and malnutrition due to eating disorders, as it may be possible to intervene sooner if the diagnosis is made earlier. Treatment of AN (in those who are underweight) and atypical AN (in those who are not underweight) is aimed at cessation of restrictive thoughts and behaviors, restoration of appropriate nutrition and weight, and normal functioning of the body. While eating disorder thoughts and behaviors are helped by both therapy and nutrition, regular functioning of the body, including regular menstruation, is linked to both appropriate nutrition and weight. Patients who are not underweight based on their body mass index (BMI) may still have oligo/amenorrhea due to their caloric restriction; thus any patient who has irregular menses should have a detailed dietary evaluation as part of their workup. Timely diagnosis and treatment of patients with eating disorders and amenorrhea is important due to the impact on bone mass accrual for adolescents who have prolonged amenorrhea. Menstrual abnormalities may also be seen in patients with bulimia nervosa (BN).