OBJECTIVE: Sleeping in the supine position has an important role in the severity and development of sleep apnea. Significant increase in the Apnea-Hypopnea Index (AHI) in cases with Positional Obstructive Sleep Apnea Syndrome (OSAS) seen in the side-lying position and in those sleeping in the supine position with moderate total AHI index scores, induce striking decreases in oxygen saturation. This condition is crucial in the emergence of OSAS-related complications secondary to hypoxemia. The objective of this study is to compare the incidence of comorbidities, and polysomnographic findings in cases diagnosed as positional OSAS, and those with different degree study. RESULTS: A total of 170 patients with positional OSAS, with a mean age of 49.4 years, were included. Patients were divided according to their AHI values as mild (AHI=5-15, n=37) and moderate-severe OSAS patients (AHI >15, n=133). There were no differences between the two groups as to concomitant conditions (hypertension, congestive heart failure, coronary artery disease, cerebrovascular disease), Epworth Sleepiness Score (ESS) and average oxygen saturation. CONCLUSION: Lack of differences in the rates of additional disorders between the two groups may indicate OSAS related complications that developed in patients with mild degree positional OSAS. Therefore, AHI should be evaluated in cases with OSAS sleeping in every lying position. Cases with positional OSAS should be evaluated as a different clinical entity and the treatment plan should be made accordingly. Thus, development of OSAS related complications could be prevented in the earlier stages. © 2014 by Turkish Thoracic Society.