This study investigates arterial stiffness changes after acute exercise in young patients with untreated, recently diagnosed grade I essential hypertension (UH) compared with normotensive (NT) individuals and the effect of antihypertensive treatment on this phenomenon. Study 1 consisted of 25 UH and 15 NT patients. UH patients who received treatment were included in study 2 and were followed-up after a 3-month treatment period with an angiotensin II receptor blocker. Aortic pulse wave velocity (PWV) was assessed at baseline, at maximal exercise, and at 10, 30, and 60 minutes later. In UH patients, PWV increased significantly at maximal exercise and 10 and 30 minutes of recovery, despite blood pressure fall to baseline levels. No significant PWV changes were observed in NT patients. Post-treatment PWV levels were significantly decreased and similar to those of NT patients. Arterial stiffness is impaired following high-intensity acute exercise even in the early stages of hypertension. Antihypertensive treatment ameliorates these effects.