Idiopathic environmental intolerance (IEI) is an acquired condition with multiple symptoms associated with diverse environmental factors tolerated by most persons, not explained by known medical or psychiatric disorders. Data from clinical and epidemiologic samples show a robust association between IEI and lifetime psychiatric disorder, particularly mood, anxiety, somatoform, and personality disorders. IEI has not been associated with lifetime substance use disorders or psychotic disorders. The relationship of IEI and psychiatric disorder is important to acknowledge because it alerts clinicians to the fact that many persons diagnosed with IEI suffer treatable emotional illnesses, and because it suggests that some persons with mental illness are being misdiagnosed when their symptoms are misinterpreted as evidence of IEI.