Forty-two female patients with an eating disorder and major depression were compared with 48 female patients with major depression in a retrospective chart study for the prevalence of thyroid disease and laboratory thyroid function abnormalities in the absence of thyroid disease. Eating disorder patients, aged 30-80 years, had a significantly higher incidence in thyroid diseases (53%) then those with major depression alone (17%). The incidence of thyroid disease did not differ between the two groups among patients aged 11-29 years. Abnormal thyroid screening values occurred in 40% of euthyroid eating disorder patients and 34% of those with major depression. While the overall prevalence of thyroid disease in depressed females (15%) was similar to that in the general population (10.5%), thyroid disease in the eating disordered/depressed patients was twice the rate expected (24%) in the general population. Female patients who require psychiatric hospitalization should be routinely evaluated for thyroid function, especially those diagnosed with an eating disorder and depression.