Hypertension is a major risk factor for cardiovascular disease. About forty million people are estimated to have hypertension. But, only 50% of hypertensive patients achieve well control of blood pressure. To prevent cardiovascular disease, more careful attention to hypertension is needed. Diagnostic level for hypertension in clinic is > or = 140/90mmHg. On the other hand, home blood pressure and 24-h ambulatory blood pressure are necessary for distinguish masked hypertension, white coat hypertension and sustained hypertension. Blood pressure is classified into optimal, normal and high-normal, and the corresponding levels are classified into grade I, grade II and grade III hypertension, respectively. Hypertensive patients are stratified into low-, moderate- and high-risk groups according to the presence or absence of risk factors other than blood pressure, hypertensive target organ damage and cardiovascular disease. In particular, the presence of diabetes mellitus and chronic kidney disease increases the risk. Attention to metabolic syndrome including a high-normal pressure as a component is also necessary. The treatment program should be prepared according to stratification of the risk; all patients must be guided to modify their lifestyle, and hypertensive medication should be started if necessary to achieve the target blood pressure level. In this paper most recommended timing to start medication for hypertensive patients is discussed.