The study investigates relationship between simple renal cyst enlargement studied by ultrasonography and anti-hypertensive treatment. To this purpose we enrolled 42 patients with newly diagnosed hypertension affected by simple renal cysts. Fourteen were randomly assigned to treatment with ACE-Inhibitors (group 1), twelve to diuretics (group 2) and sixteen to Ca-Antagonists (group 3). Patient performed a basal ultrasonography to evaluate basal cyst dimension before starting anti-hypertensive treatment. Following 12 months of the anti-hypertensive regimen, a new echograph was performed to evaluate changes in cyst size. A control group consisting of 15 patients with normal blood pressure and simple renal cysts was enrolled (group 0). An enlargement of cysts was detected in all patients. However, the enlargement observed in patients treated by Ca-Antagonists was significantly greater than that observed in the other groups (p<0.05). Our study supports the hypothesis that Ca-Antagonists may favor cyst enlargement by enhancing cyclic AMP production. In fact, cAMP and cAMP agonists stimulate fluid secretion by lining cells of the cyst wall, inducing cyst enlargement.