Diabetes and hypertension frequently coexist, leading to additive increases in the risk of life-threatening cardiovascular events. Hypertension is a common comorbid condition in patients with type 1 or type 2 diabetes when compared with the general population and occurs in 75% of patients with the more prevalent form of diabetes, type 2. Arterial blood pressure plays an important role in the development of renal damage and presents a complex relationship. It is well-known that hypertension accelerates the course of microvascular and macrovascular complications of diabetes and that hypertension often precedes type 2 diabetes and vice versa. Patients with type 1 and 2 diabetes and nephropathy frequently have circadian changes in blood pressure that correlate to nephropathy risk. Early detection of nocturnal hypertension and early intervention with angiotensin blockade may delay progression of diabetic nephropathy.