Abstract: Background Orthostatic hypotension may cause fall,fracture,cardiocerebrovascular events and death.Objective To determine the prevalence and risk factors of orthostatic hypotension in a community-based middle aged and old hypertensive population.Methods This cross-sectional study was conducted in 5101 hypertensive patients aged 40 to 75 years in 7 communities of Xinyang county.The orthostatic blood pressure was measured in supine position after resting for more than 5 minutes and at 0 and 2 min after standing.Orthostatic hypotension was defined as 20 mmHg or greater decrease in SBP or 10 mmHg or greater decrease in DBP.Results The prevalence of orthostatic hypotension was 23.8% at either 0 or 2 min after standing（20.1% or 17.2%,respectively） in middle aged and old hypertensive patients.Orthostatic hypotension was significantly increased with age（40-49 years: 11.8%,50-59 years: 16.1%,60-75 years: 18.3%,P=0.004） in women.No significant difference was found between treated and untreated hypertensive patients（P＞0.05）.After adjustment for age,gender,BMI,antihypertensive treatment,logistic regression analysis showed that coronary heart disease（OR: 1.78,95% CI: 1.30-2.48,P＜0.01）,previous stroke（OR: 1.40,95% CI: 1.06-1.90,P=0.034）,supine blood pressure,sitting blood pressure and heart rate（OR: 0.98,95% CI: 0.98-0.99,P=0.001） were predisposing determinants for orthostatic hypotension.Conclusions Orthostatic hypotension is common in middle and old hypertensive patients which increased with age in women.Comorbid cardiovascular disease,but not antihypertensive treatment,may increase the risk of orthostatic hypotension.