The definitive diagnosis of hypertension based on home blood pressure (BP) monitoring (HBPM) results may be practical, particularly in the primary care setting; however, some hypertensive patients are overlooked by HBPM alone. It is unclear which HBP cutoff value should set for patients who require ambulatory BP monitoring (ABPM). In the present study, home systolic BP (SBP) data (6 BP measurements taken for 3 days in the morning and evening) and 24-h ambulatory SBP data from 462 hypertensive subjects were obtained from a real-world clinical study. Using HBPM as an initial step for the definitive diagnosis of hypertension, 381 of 462 total subjects had a home SBP value of 135 mm Hg. Of these 381 subjects, 90.3% had ambulatory SBP values of 130 mm Hg. Among the other 81 subjects with home SBP values of <135 mm Hg, 60.5% had ambulatory SBP values of 130 mm Hg ('true uncontrolled hypertension'). These percentages differed significantly (P<0.0001). The cutoff home SBP value of 135 mm Hg could discriminate between subjects who did not require ABPM (home SBP value of 135 mm Hg) and those who did (home SBP value of <135 mm Hg) for the diagnosis of true uncontrolled hypertension.