Background: Thyroid gland dysfunction affects the structure and function of the heart. Tissue Doppler echocardiography is a new technique, and it has been used frequently in the evaluation of ventricular function. In the present study, right ventricular function was assessed in patients with overt or subclinical hypothyroidism and hyperthyroidism and in healthy subjects using the tissue Doppler method, and results were compared. Patients and Methods: 20 healthy subjects and 63 patients diagnosed with overt and subclinical hypothyroidism and hyperthyroidism were included in the study. Annular and myocardial systolic peak velocities, early and late diastolic peak velocities, precontraction, total contraction and relaxation times of the right ventricle were recorded by tissue Doppler echocardiography. The results of the patients were compared to those of the controls. Results: Myocardial systolic velocity was significantly higher in patients with hyperthyroidism. Annular and myocardial late diastolic velocities were found to be significantly lower in patients with overt hypothyroidism. Annular precontraction time was increased in patients with overt and subclinical hypothyroidism. Myocardial precontraction time was decreased in patients with hyperthyroidism, and increased in patients with overt hypothyroidism patients. Annular relaxation time was increased in patients with overt hypothyroidism. Conclusions: Right ventricular function is affected in patients with thyroid diseases. The tissue Doppler technique is a suitable tool to detect impairments in right ventricular function. There is a significant correlation between serum thyroid hormone levels and right ventricular velocities and time intervals.