Isolated systolic hypertension (ISH) is a definite risk factor for cardiovascular complications (i.e., cardiac failure, coronary artery disease, and stroke) independent of diastolic elevation. The prevalence of ISH is estimated to be approximately 15-20% in the population above the age of 60 years, and increases with advancing age. The Systolic Hypertension in the Elderly (SHELL) study is planned to evaluate the efficacy and tolerability of lacidipine, matched with the diuretic chlorthalidone, in treatment of ISH in elderly hypertensive patients (EHP). One hundred fifteen Italian centers will participate in the study. Fifty centers are associated with the Società Italiana di Geriatria Ospedaliera and 65 centers are departments of internal medicine or outpatient clinics for management of hypertension. A total of 4,800 patients will be enrolled in the trial. Two subprojects will consist of periodical echocardiographic evaluation and 24-h ambulatory blood pressure monitoring. The primary end point of the SHELL study is the incidence of cardiovascular and cerebrovascular events in EHP with ISH, treated with either lacidipine or chlorthalidone. In particular, the SHELL trial is intended to determine whether lacidipine treatment will significantly reduce fatal myocardial events and total cardiovascular mortality.