Subclinical hypothyroidism (SCH) has been reported to occur in patients with a variety of affective syndromes. However, the clinical correlates of SCH in patients with major depression have received limited attention. We therefore examined demographic, clinical and treatment response variables in a cohort of patients with unipolar, nonpsychotic major depression with and without SCH. Of 139 subjects, 19 had SCH defined as an elevated basal TSH with normal circulating levels of T3 and T4. Major depression with SCH differed from that without SCH by the presence of a concurrent panic disorder and a poorer antidepressant response.