A factitious disorder is a condition in which a person, without a malingering motive, acts as if they have an illness by deliberately producing, feigning, or exaggerating symptoms, purely to attain (for themselves or for another) a patient's role. People with a factitious disorder may produce symptoms by contaminating urine samples, taking hallucinogens, injecting fecal material to produce abscesses, and similar behaviour.

Factitious disorder imposed on self (also called Munchausen syndrome) was for some time the umbrella term for all such disorders. Factitious disorder imposed on another (also called Munchausen syndrome by proxy, Munchausen by proxy, or factitious disorder by proxy) is a condition in which a person deliberately produces, feigns, or exaggerates the symptoms of someone in their care. In either case, the perpetrator's motive is to perpetrate factitious disorders, either as a patient or by proxy as a caregiver, in order to attain (for themselves or for another) a patient's role. Malingering differs fundamentally from factitious disorders in that the malingerer simulates illness intending to obtain a material benefit or avoid an obligation or responsibility. Somatic symptom disorders, though also diagnoses of exclusion, are characterized by physical complaints that are not produced intentionally.