Backgrounds: In hypertensive patients, target organ damage (TOD) is closely related to morbidity and mortality. Early detection of TOD is important to improve outcome. The aim of this study is to elucidate clinical factors related to TOD in patients with hypertension. Methods: From June 2006 to March 2007, 1087 patients with essential hypertension (mean age = 56.9 짹 9.6, male = 47.7%) in 9 centers were included. We stratified these patients to 6 groups according to their age and sex. The clinical factors influencing TOD were assessed by multivariate Logistic regression analysis. Results: Mean values of blood pressure, body mass index, waist circumference, fasting blood sugar, total cholesterol, LDL cholesterol, HDL cholesterol and triglyceride were 138.50 / 82.65 mmHg, 25.10 kg/m2, 87.58 cm, 106 mg/dL, 180.76 mg/dL, 101.92 mg/dL, 51.55 mg/dL and 138.78 mg/dL. The proportion of patients with smoking, physical inactivity, family history of cardiovascular disease and CRP more than 1 mg/dL were 14.4%, 31.3%, 9.5% and 16.5%. Three hundred and fifty nine patients had TOD (total 33.0%, heart disease 30.1%, cerebrovascular disease 2.5%, chronic renal disease 0.3%, peripheral artery disease 0.5%, retinopathy 0.8%, carotid atheroma 4.8%). Family history in the young-aged male group (age < 45), physical inactivity in the middle-aged male group (45 ��� age < 65), systolic BP and physical inactivity in the old-aged male group (age ��� 65) were significantly related to TOD (Table 1). Conclusion: Clinical factors related to TOD in hypertensives are different according to their ages. These factors can be used for preventing TOD.