To investigate the underlying mechanisms of asymptomatic cerebrovascular damage, the diurnal change in blood pressure was evaluated in hypertensive patients with silent cerebral infarction (SCI). Sixty elderly hypertensive patients (age > or = 60 years) were matched with 40 middle-aged patients (age < or = 59 years) for sex and left ventricular mass index (LVMi). Lacunar lesions were evaluated by magnetic resonance imaging as SCI. The presence and the severity of SCI increased with age. In the middle-aged group, the presence of SCI was significantly related to 24-h blood pressure and LVMi evaluated by echocardiography. In elderly patients, the presence of SCI had no relationship with 24-h blood pressure or LVMi. The lowest level of nocturnal diastolic blood pressure showed a J-shaped relationship with the incidence of SCI in the elderly patients. These findings indicate that the hemodynamic characteristics underlying the development of SCI differ between middle-aged and elderly hypertensive patients. A different approach to the treatment of hypertension in the elderly appears necessary.