Obstructive sleep apnea syndrome (OSAS) is a widespread disorder characterized by recurrent, partial, or complete episodes of apnea due to upper airway tract obstruction during sleep. OSAS frequency is likely to increase in hypothyroidism because of obesity, macroglossia, dysfunctional upper respiratory tractus (URT) musculature, deposition of mucopolysaccharides in URT tissues, and decreased ventilatory control. This study examines the relationship between OSAS and thyroid disease in OSAS subjects. This study includes 150 polysomnographically diagnosed OSAS patients (50 mild, 50 moderate, 50 severe OSAS cases) treated at Endocrinology and Metabolism Department of Ankara Numune Training and Research Hospital between January 2010 and May 2011 and 32 non-OSAS control subjects. All patients were given serum TSH, free T3 (fT3), free T4 (fT4), anti thyroid peroxidase (Anti-TPO), and anti-thyroglobulin (anti-TG) tests, as well as thyroid ultrasounds. We did not find any difference in prevalence of hypothyroidism, numbers of nodules and parenchyma heterogenicity determined by ultrasound, between OSAS subgroups and controls (p > 0,05). In this study, functional and ultrasonographic examination of the thyroid gland did not reveal any relationship between OSAS and thyroid disease. We believe hence that long-term follow-up studies can establish the possible significance of routine evaluation of OSAS patients for thyroid disease.