Background: White coat effect (WCE) is that blood pressure (BP) measured by a medical professional in a medical setting tends to be elevated in comparison with BP measured by the patients themselves at home. Hypothesis: We performed this study to evaluate the affecting and predicting factors of white coat effect in treated hypertensive patients in Korea. Methods: A total of 1,087 outpatients (57짹10 years, female; 52%) with chronically treated hypertension in university hospitals were enrolled. Home BP was checked in every morning and evening for 2 weeks. WCE was defined as a positive difference of physician���s BP-home BP. We evaluated the association of WCE with age, gender, potential vascular risk factors, target organ damage, systolic and diastolic BP, mean BP, heart rate, and pulse pressure. Results: The averages of WCE were 9.8짹14.8 mmHg in systole and 3.4짹9.2 mmHg in diastole. There was no significant association with age and gender. Family history of premature cardiovascular disease (r=0.061, p=0.045 in systole, r=0.079. p=0.010 in diastole) were positively correlated with WCE. Diabetes mellitus (r=-0.066, p=0.030 in systole, r=-0.076, p=0.013 in diastole) and smoking (r=-0.068, p=0.026 in systole, r=-0.069, p=0.022 in diastole) were negatively correlated in WCE. Target organ damages including heart were also negatively associated with WCE (r=0.095, p=0.002 in systole, r=-0.089, p=0.004 in diastole). Pulse pressure by physician was positively correlated with WCE (r=0.511, p<0.001 in systole, r=0.063 p= 0.037 in diastole). By multi-variate regression analysis, pulse pressure by physician was independently correlated with systolic WCE (��=0.573, p<0.001) and diastolic WCE (��=0.092, p<0.001). Conclusions: Although pulse pressure has been known to be a mechanical property of large arteries, it was also associated with WCE. Our findings suggest that pulse pressure measured by physician at clinic may predict the WCE, which may help control the treated hypertensive patients.