Obstructive sleep apnea syndrome (OSAS) is an independent risk factor for the development of cardiovascular events and hypertension. Mean platelet volume (MPV), an indicator of platelet activation and aggregation, is closely related with cardiovascular diseases (CVDs). We aimed to show the relationship between OSAS and MPV with CVD. The medical records of 205 patients who were admitted to the sleep study were evaluated. OSAS was diagnosed by polysomnography if the apnea-hypopnea index (AHI) was greater than 5. MPV was calculated from blood samples. According to AHI, individuals in whom AHI was less than 5 were recruited as the control group, those in whom AHI was 5-15 as the mild OSAS group, those in whom AHI was equal to 15-30 as the moderate OSAS group, and those in whom AHI was greater than 30 as the severe OSAS group. Of the patients, 137 (67%) were men and 68 (33%) were women; the mean age was 53.0 +/- 14.1 years. There were 35 (17%), 20 (10.2%), 42 (20.4%), and 108 (52.6%) participants in groups 1, 2, 3, and 4, respectively. There were significant differences in terms of coronary artery disease and hypertension between all groups (P<0.05). There was a significant association between the severity of OSAS and MPV in groups 3 and 4, whereas there was not any association in groups 1 and 2 (group 1=9.3 +/- 0.7, group 2=9.4 +/- 0.8, group 3=9.5 +/- 1.1, group 4=10.2 +/- 1.2; P for trend 0.03). We showed that MPV was significantly increased in patients with OSAS, which is an independent risk factor for CVD. Therefore, MPV could be used as a marker to predict CVD in OSAS. (C) 2013 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.