Aim; The severity of airway obstruction in chronic obstructive pulmonary diseases (COPD) is associated with impairment of thyroid gland function. Methods; We evaluated thyroid abnormalities in patients with COPD and relationship between pulmonary function tests, arterial blood gases and thyroid functions. Results; There was no significant difference in mean levels of TSH, FT3 and FT4 between COPD and control group. Serum level of TSH was lower than normal limits in 20 of 62 patients with COPD. Serum level of FT3 was higher than normal limits in 2 of 20 patients with lower TSH level. In control group, TSH was lower than normal limits in 2 patients, but FT3 was normal in these patients. There was significant difference according to percentage of cases with TSH less than minimum values and FT3 higher than maximum values between COPD and control group. Conclusion; we have demonstrated that both clinic and subclinic hyperthyroidism were higher in patients with COPD exacerbations than cases without COPD.