Summary. Arterial hypertension is frequently associated with type 2 diabetes mellitus, and both of these diseases are the major risk factors for cardiovascular complications. During the past few years, a number of large randomized clinical trials examined the frequency of new onset diabetes mellitus during administration of antihypertensive drugs. Application of ACE inhibitors or angiotensin receptor blockers reduces the risk for the onset of diabetes mellitus by 20–27%, and calcium channel blockers by 16%. Despite some uncertainties, novel studies have demonstrated an increased risk for cardiovascular complications related to new onset diabetes mellitus. The duration of patient monitoring is also an important factor, as the onset of diabetes-related complications is closely associated with the duration of this disease. Considering all above, the aim of preventing the onset of diabetes is to recognize patients with an increased risk. The risk factors include basal glycemia, positive family history for diabetes mellitus, obesity, metabolic syndrome, and some ethnic groups (South Asia, the Caribbeans). Therefore, increased-risk patients should be subjected to therapy with ACE inhibitor, angiotensin receptor blocker, or calcium channel blocker as the first drug of choice. For these patients, application of thiazides and beta blockers or the combination of these two drugs is not advantageous. However, such a view poses a dilemma whether thiazide diuretics should be the first choice in the treatment of hypertension.