Body dysmorphic disorder (BDD), occasionally still called dysmorphophobia, is a mental disorder characterized by the obsessive idea that some aspect of one's own body part or appearance is severely flawed and therefore warrants exceptional measures to hide or fix it. In BDD's delusional variant, the flaw is imagined. If the flaw is actual, its importance is severely exaggerated. Either way, thoughts about it are pervasive and intrusive, and may occupy several hours a day, causing severe distress and impairing one's otherwise normal activities. BDD is classified as a somatoform disorder, and the DSM-5 categorizes BDD in the obsessive–compulsive spectrum, and distinguishes it from anorexia nervosa.

BDD is estimated to affect from 0.7% to 2.4% of the population. It usually starts during adolescence and affects both men and women. The BDD subtype muscle dysmorphia, perceiving the body as too small, affects mostly males. Besides thinking about it, one repetitively checks and compares the perceived flaw, and can adopt unusual routines to avoid social contact that exposes it. Fearing the stigma of vanity, one usually hides the preoccupation. Commonly unsuspected even by psychiatrists, BDD has been underdiagnosed. Severely impairing quality of life via educational and occupational dysfunction and social isolation, BDD has high rates of suicidal thoughts and attempts at suicide.