We studied 13 untreated Graves' disease subjects in a clinical research unit using endocrine, psychiatric, and neuropsychological assessments. We used SADS interviews, RDC, standardized symptom rating scales, and motor activity monitoring to update earlier studies and quantified psychiatric symptoms to elucidate any correlations between endocrine and psychiatric status. Nine of 13 subjects had major depression, 8/13 had generalized anxiety disorder, and 3/13 were hypomanic. Anxiety levels were much higher than in other hospitalized medical patients. Using a broad battery of neuropsychological testing, we found mild deficits in attention, memory, and complex problem solving that were consistent with previous studies of hyperthyroid patients. The severity of psychiatric symptoms could easily result in an inappropriate referral to a psychiatrist prior to the diagnosis of hyperthyroidism. The relationship between psychiatric symptoms and possible CNS effects of excess levels of thyroid hormone is discussed.