Patients with diabetes mellitus are more frequently hypertensive than age-matched non-diabetic subjects. They are confronted with a markedly increased risk of coronary vascular disease, of progressive nephropathy and renal end-stage diseases. The most common type of hypertension in type I and type II diabetics is essential hypertension, probably as a consequence of insulin resistance and hyperinsulinemia. Hyperglycemia and hypertension are both significantly involved in the progression of diabetic nephropathy. Hence, the modern therapeutic concept consists of optimal blood glucose control and strict blood pressure control. Progression of the nephropathy may be halted in most of the cases by adhering to set limits in mean arterial blood pressure, glycated hemoglobin and urinary albumin excretion rate. Furthermore, a significant decrease in cardiovascular mortality may be achieved. In case the blood pressure targets cannot be met by non-drug therapies and life-style modifications, antihypertensive drug therapy has to be initiated. The selection of antihypertensives should be based on the concomitant diabetes mellitus with its additional cardiovascular risk factors hyperlipidemia and hyperinsulinemia. In general, preference should be given to so-called metabolic neutral substances such as ACE inhibitors or calcium antagonists or to alpha-blockers which may have positive metabolic effects. Meanwhile, data from several prospective studies claim that ACE inhibitors and calcium antagonists exert nephroprotective effects beyond their beneficial blood pressure lowering effects, thereby preventing the progression of diabetic nephropathy. However, these drugs should not be uncritically used and we should be aware of their potential adverse effects. The differential therapy of hypertension in diabetes mellitus requires mature consideration before initiation of therapy, an individualized concept of therapy, and careful monitoring during treatment.