Background. Obstructive sleep apnea (OSA) syndrome is one of the most common respiratory disorders in humans. There is emerging evidence linking OSA to vascular disease, particularly hypertension. The underlying pathophysiological mechanisms that link OSA to cardiovascular diseases such as hypertension, congestive heart failure, and atrial fibrillation are not entirely understood. The aim of this study was to investigate the association of obstructive sleep apnea hypopnea syndrome (OSAHS) with coronary atherosclerotic disease (CAD). Methods. A questionnaire survey based on Berlin questionnaire and Epworth Sleepiness Scale (ESS) was conducted among 406 patients to assess demographic data and the symptoms, such as excessive daytime sleepiness and snoring. Epworth Sleepiness Scale and Berlin questionnaire were completed by all of the patients. Venous blood samples were obtained for biochemical tests. Characteristics of coronary arteries were collected from angiographies' reports. All patients were divided into two groups based on results from Berlin questionnaire: low risk patients for OSA and high risk patients for OSA. Data were analyzed by SPSS software version 13. Results. Mean age of patients was 61.8 ± 10.5. 212 (52.2%) patients were categorized as high risk group for apnea. Also, excessive daytime sleepiness was reported in 186 patients (45.8%). The severity of coronary artery involvement, daytime sleepiness, and electrocardiogram abnormalities was significantly higher in high risk patients for OSA compared with low risk patients. High risk patients had higher level of FBS and LDL and lower level of HDL cholesterol (P < 0.05). Conclusion. Our study found a strong correlation between the number of stenotic vessels and OSA. Based on our findings, OSA can be a predisposing factor for cardiac diseases.