: Obstructive sleep apnea (OSA) is a common chronic disorder with increased morbidity and mortality. Asymptomatic LV diastolic dysfunction is also a common condition with many interrelated risk factors. To investigate the prevalence of diastolic dysfunction among obstructive sleep apnea patients and the impact of its severity on diastolic dysfunction grade. Fifty patients with obstructive sleep apnea confirmed by Home Sleep Apnea Testing (HSAT). The diastolic function of the left ventricle determined by Doppler echocardiography. Baseline characteristics, the severity of obstructive sleep apnea, and diastolic dysfunction severity are compared. The median age is 45 years. Most patients (n = 37, 74%) were male. Thirty-six (72%) patients were hypertensive. The Mean Body Mass Index (BMI)was 29 kg/m2. Fifteen patients (30%) were current smokers. The mean apnea-hypopnea index (AHI) was 33±12 events/hour and most patients had severe OSA, with AHI>30 events/hour (n = 26, 52%). Diastolic dysfunction prevalence is 72% (n=36 patients). Only hypertension is significantly associated with diastolic dysfunction (p-value 0.004) with no significant association with age, gender, diabetes mellitus, Body Mass Index (BMI) and smoking status. Diastolic dysfunction grade has a significant association with the AHI, OSA severity and minimum SpO2 (p-values 0.000, 0.028 and 0.000, respectively). Diastolic dysfunction is prevalent in OSA patients with many related risk factors. Hypertension significantly associated with diastolic dysfunction and Diastolic dysfunction grade has a significant association with the apnea-hypopnea index (AHI), OSA severity and minimum SpO2.