Bulimia nervosa, also known simply as bulimia, is an eating disorder characterized by binge eating (eating large quantities of food in a short period of time, often feeling out of control) followed by compensatory behaviors, such as self-induced vomiting or fasting, to prevent weight gain.

Other efforts to lose weight may include the use of diuretics, laxatives, stimulants, water fasting, or excessive exercise. Most people with bulimia are at normal weight and have higher risk for other mental disorders, such as depression, anxiety, borderline personality disorder, bipolar disorder, and problems with drugs to alcohol. There is also a higher risk of suicide and self-harm.

Bulimia is more common among those who have a close relative with the condition. The percentage risk that is estimated to be due to genetics is between 30% and 80%. Other risk factors for the disease include psychological stress, cultural pressure to attain a certain body type, poor self-esteem, and obesity. Living in a culture that commercializes or glamorizes dieting, and having parental figures who fixate on weight are also risks.

Diagnosis is based on a person's medical history; however, this is difficult, as people are usually secretive about their binge eating and purging habits. Further, the diagnosis of anorexia nervosa takes precedence over that of bulimia. Other similar disorders include binge eating disorder, Kleine–Levin syndrome, and borderline personality disorder.