The coexistence of hypertension and diabetes increases the incidence of cardiovascular events and long-term morbidity and mortality. Blood pressure should be controlled with the most appropriate drugs as well as tight blood glucose control in patients with diabetes and hypertension. RAAS (Renin Angiotensin Aldosterone System) blockers have an important role in the treatment of these patients, in this sense, ACEi and ARB remained the major treatment option in hypertension guidelines. The most recent RAAS blocker to be approved by the FDA was aliskiren in 2007, a renin inhibitor. Studies showed that aliskiren is as effective as other antihypertensive drugs and has a safety profile similar to placebo. The potent renin inhibitor aliskiren directly inhibits the RAAS system at its rate limiting step and differently from other RAAS blockers; it decreases plasma renin activity (PRA). Although the relationship of increased PRA levels and cardiovascular risk has been shown, it is unclear if the PRA decrease provided by aliskiren has an impact on clinical outcomes and cardiovascular endpoints. On the other hand, large trials like ASPIRE, AVANT-GARDE, ALTITUDE, ASTRONAUT, which investigated the combination of aliskiren with other RAAS blockers, failed to show the expected outcomes or resulted with an increased incidence of adverse effects, which raised more questions. As a result of the ALTITUDE trial, combination of aliskiren with an ACEi or ARB is not recommended in patients with hypertension and diabetes, or at least moderate renal dysfunction. Trials designed to prove aliskiren's efficacy in new indications like diabetes, may face similar problems related to dual RAAS blockade because in the majority of cases, the optimal treatment is achieved with an ACEi or ARB. In this conjuncture, the increase in adverse events seen with aliskiren might be related to dual RAAS blockade rather than aliskiren directly. For instance, it is unclear whether the adverse event incidence would be the same, less, or higher if ALTITUDE was designed to investigate ACEi and ARB combination without aliskiren. In fact, every new molecular entity and mechanism of action faces the same barriers. For the time being, differentiating points like PRA lowering effects as an add-on therapy to calcium channel blockers or hydrochlorothiazide, and the populations that might have additional benefit, should be carefully investigated.