Anorexia nervosa is a common eating disorder that usually begins at the age of fourteen or fifteen, with another peak in incidence in eighteen year olds. It is more common in adolescent girls (affecting almost 1% of adolescent females), but it is also found in boys and its incidence has been increasing. Anorexia causes an overwhelming fear of being overweight and a drive to be thin, leading to a restriction of calories that can lead to being underweight.

Teens with anorexia may also have bulimia nervosa, with a loss of control and binge eating, followed by purging behaviors.

It is not known what causes eating disorders, but it does seem to be associated with certain genetic attributes and it is more common in children who have a first-degree relative with an eating disorder. Other factors that put you at risk for an eating disorders is participating in certain competitive activities (especially ballet, skating, athletics, and fashion modeling,), having a perfectionist or obsessive personality, and having a parent with an eating disorder or weight problem (obesity, frequent dieting).

Eating disorders are probably also more common in children with a past history of physical or sexual abuse.