Obstructive sleep apnea syndrome (OSAS) is a common disorder and in subjects with OSAS the prevalence of hypothyroidism is approximately 1.2-11 %. The episodes of hypoxia/reoxygenation associated with the respiratory disturbances observed in subjects with OSAS increases the risk of cardiovascular diseases. Hypothyroidism; primary or subclinical, has several effects on cardiovascular system. In our study, we investigated carotid artery intima-media thickness (IMT) which is an early sign of atherosclerosis, in OSAS subjects with hypothyroidism. Subjects who admitted to Kahramanmaras Necip FazA +/- l City State Hospital Chest Diseases out-patient clinic between May 2014 and January 2016 for snoring and had polysomnographic evaluation at the sleep laboratory were included in this study. Each subject was evaluated for serum thyroid function tests and carotid artery IMT was measured by a Doppler ultrasound. Mean carotid artery IMT values in the isolated OSAS, OSAS plus hypothyroidism, and control groups were 0.67 +/- 0.12, 0.8 +/- 0.12, and 0.54 +/- 0.08 mm, respectively; difference between groups was statistically significant (p < .05). A poXsitive correlation was found between thyroid stimulating hormone levels and IMT (r = 0.426, p = .002), while free T3 levels and IMT were negatively correlated (r = -0.463, p = .001). IMT and apnea-hypopnea index were also positively correlated (r = 0.403, p = .003). We suggest, physicians should be alert for hypothyroidism comorbidity in OSAS, and suspected subjects with OSAS should be screened for hypothyroidism considering the potential cardiovascular complications.