Background: 24-h ABPM is superior to official or home-monitored blood pressure(BP) values in assessing the circadian rhythm of BP. Recently, the early morning surge (EMS) has been reported to be associated with cardiovascular events, including myocardial infarction and stroke. The aim of this study was to investigate the relationship between the 24-h ABPM and conventional cardiovascular risk factors. Method: Untreated 346 patients (mean age: 48짹12yrs, M:F=175:171) diagnosed as essential hypertension (defined as 24-h mean ambulatory systolic BP���125 mmHg or diastolic BP���80 mmHg) without any other cardiovascular risk factors such as diabetes mellitus, dyslipidemia or nephropathy (serum creatinine more than 2.0mg/dl) were enrolled. Early morning systolic BP was defined as the mean systolic BP reading during the first 2 hours after the subject awakes. The lowest night systolic BP was the mean systolic BP reading across 3 consecutive measurements, including the middle value as the lowest systolic BP reading recorded during the night. EMS was defined as early morning systolic BP minus the lowest night systolic BP. We compared the 24-h ABPM parameters in 2 groups divided by age of 60. Results: 1. EMS (18.1짹14.4 : 24.0짹14.1mmHg, p=0.002), 24-h mean BP (105.3짹10.9 : 102.1짹8.5 mmHg, p=0.044), 24-h mean pulse pressure (51.7짹9.9 : 57.5짹10.6 beats per minute, p<0.001), day-time mean BP (108.7짹11.2 : 104.5짹9.2 mmHg, p=0.005), day-time mean pulse pressure (52.9짹10.4 : 58.2짹10.9 beats per minute, p<0.001), and night-time mean pulse pressure (49.7짹11.0 : 53.9짹14.6 beats per minute, p<0.001) were significantly increased in elderly subjects than young. 2. The degree of dipping (9.6짹7.7 : 7.2짹9.5%, p=0.002) was decreased in elderly subjects than young. 3. Age was an independent risk factor for highest quartile of EMS (>28 mmHg) after adjusting gender difference and body mass index [p=0.001, odd ratio (95% confidence interval), 1.043 (1.018-1.068)]. Conclusion: The BP control of the early morning period is more important in elderly patients to prevent cardiovascular events.