We evaluated thyroid function (T3, T4, TSH) and TRH Test in 17 patients with obsessive-compulsive disorder (DSM III criteria and at least 1 year duration) not associated to major depression (absence of DSM III criteria and depression Hamilton scale score, 17 items, below 16). Blood tests were performed following a drug-free period of at least 2 weeks. We accidentally discovered one case of hyperthyroidism with the diagnosis of Graves' disease. In the remaining group (n = 16), basal values of thyroid hormones and TSH were normal. 12.5% (2 cases) showed a blunted delta TSH (less than 5 mUl/l) and 0% a high delta TSH (greater than 20 mUl/l). A significant degree of negative correlation was only noted between delta TSH and age (r = -0.65). Lastly, we report a curious comorbidity between OCD and Graves' disease found in 3 cases within a population of 50 OC patients (or 6%) recruited in our psychiatric unit. The characteristics of these observations will be presented.