This is not as simple to answer as it may seem. In general, the higher the blood pressure, the greater the risk to health. Depending on various factors, the level at which blood pressure is said to be high (hypertension) can vary from person to person. The cut-off point for blood pressure that is said to be high is 140/80 mm Hg or above for people with diabetes and 130/80 mm Hg for those with diabetes and complications (for example, kidney disease). These are lower than the cut-off point for people who do not have diabetes. The cause is not known in most cases. This is called essential hypertension. The pressure in the blood vessels depends on how hard the heart pumps, and how much resistance there is in the blood vessels (arteries). It is thought that slight narrowing of the arteries increases the resistance to blood flow, which increases the blood pressure. The cause of the slight narrowing of the arteries is not clear. Various factors probably contribute. (It is a bit like water in a hosepipe. The water pressure is increased if you open the tap more but also if you make the hosepipe narrower by partially blocking the outflow with your thumb.) Diabetic kidney disease (diabetic nephropathy) is a complication which develops in some people with diabetes. In this condition the kidneys are damaged, which can cause high blood pressure. This is more common in people with type 1 diabetes. Rarely, high blood pressure is caused by other conditions. It is then called secondary hypertension. For example, certain kidney or hormonal problems can cause high blood pressure. There is now plenty of good evidence from studies that controlling blood pressure in people with diabetes reduces the risk of future complications. A large research study called the UK Prospective Diabetes Study confirmed this. In this study, many people with diabetes were monitored over several years. The study found that those with well-controlled blood pressure had nearly a third less risk of dying from complications related to diabetes (heart attack, stroke, etc) compared with those with poorly controlled blood pressure. In fact, this study found that good control of blood pressure was even more beneficial than good control of the blood sugar (glucose) level to reduce the risk of developing complications from diabetes.