Hypertension is a silent, malevolent factor in both cardiovascular and renal disease. Raised blood pressure (BP) rarely causes any symptoms – in fact the presenting symptom of hypertension is too often the heart attack or stroke that is the end result. Diagnosis of prolonged abnormal blood pressure is therefore key in the prevention of a range of long-term conditions. In this article, we will examine the importance of measuring blood pressure correctly before making the diagnosis of hypertension. We will also look at the different levels of blood pressure that constitute a diagnosis of hypertension according to the variety of guidelines that exist.