This article describes the objectives and protocol of the HAROLD study, a trial designed to assess whether home blood pressure (BP), 24-hour ambulatory BP, left ventricular structure and function, and albumin excretion rate are more accurate predictors of outcome than traditional sphygmomanometric BP in elderly subjects with borderline hypertension. Development of sustained hypertension (BP > or = 160/95 mmHg) and incidence of morbid events over a 5-year follow-up are considered soft and hard endpoints, respectively. Patients with blood pressure values between 140/90 and 159/94 mmHg after three months of observation and who have never been treated, are eligible for the study; these subjects must be 60 to 79 years old, and free from other important risk factors for atherosclerosis. Baseline exams, which include plasma renin and insulin, 24-hour urine collection for detection of microalbuminuria, and echo-doppler cardiac examination are repeated after three and five years follow-up, or when subjects develop sustained hypertension. To recruit a large enough number of subjects to allow a sufficient number of endpoints (over 1000 subjects), the study is conducted as a multicenter trial. Ninety Italian Hospital Centers have agreed to participate in the study.