Severe thyrotoxicosis can cause irreversible congestive heart failure. To investigate the coincidence of subclinical thyroid disorders and idiopathic dilated cardiomyopathy (IDC) we investigated these patients with respect to their morphological and functional thyroid status. Thyroid sonography as well as thyroid hormone levels were measured in all patients. Results: Sixty-one patients (50 male, 11 female) with chronic stable IDC were included. Two out of 61 patients showed completely normal thyroid morphology and function. The other 59 patients showed either morphological or functional abnormalities or both. Of the 53 patients with morphological abnormalities 23 patients (all male) showed diffuse goiter as opposed to 29 nodular enlarged organs (24 male, 5 female). No clinically significant hypothyroidism or thyrotoxicosis was seen. A good correlation was found between the duration of IDC and thyroid volume (r = 0.44; p < 0.001). Two patients died during the study period, 1 from sudden death and 1 from progressive heart failure. Conclusion: Subclinical thyroid disorders are frequently seen in patients with long-standing IDC when they live in an area of chronic iodine deficiency. This can be explained by chronic salt restriction as basic treatment for congestive heart failure. Therefore we conclude that examination of the thyroid gland should be done routinely in patients with IDC, especially when restriction of salt intake is recommended by the treating physician.