This article is about the symptom. For the medical condition, see Anorexia nervosa.

In medicine, anorexia is the symptom of diminished appetite or appetite loss. The eating disorder anorexia nervosa is commonly referred to simply as "anorexia" in lay terminology.

Anorexia is one of the major etiologies, or causes, of malnutrition. Common disorders that cause anorexia include anorexia nervosa, severe depression , cancer, dementia, AIDS, and chronic renal disease .

Anorexia may also be seen in heart failure, perhaps due to congestion of the liver with venous blood.

Although the presenting symptom (the one which prompts a patient to seek medical attention) in acute appendicitis is abdominal pain, the presence of anorexia is requisite to making the diagnosis.