The present study intended to evaluate the variation of the hypertensive prevalence detected on a single-day blood pressure (BP) value against that on an average of 3-day BP values. This study included 1185 residents (age 21–94, 62.6 ± 14.0 years, 491 males) for BP measurements over three separate visits within a 7-day period. The newly diagnosed hypertension on the first day BP value was recorded as hypertension by epidemiological method, whereas that on the average of 3-day BP values as hypertension by clinical method. True positive rate (TPR) was the ratio of the newly diagnosed hypertensives by clinical method to those by epidemiological method. The overestimation ratio was calculated based on the following formula: (epidemiological prevalence–clinical prevalence)/epidemiological prevalence. Our results showed that of the 367 newly diagnosed hypertensives by epidemiological method, 308 were confirmed by clinical method, and with a TPR of 83.9%. The epidemiological prevalence of hypertension was higher than the clinical prevalence (41.1% vs. 36.1%) with an overestimation ratio of 12.2%. In addition, the participants aged <65 years had a lower TPR (77.9% vs. 87.8%, P = .012) against the participants aged ≥65 years. Furthermore, participants with systolic BP values of <160 mm Hg (78.2% vs. 100%, P < .001) or diastolic BP values of <100 mm Hg also had a lower TPR (70.1% vs. 100%, P = .006) compared with those having a systolic BP of 140–159 mm Hg or diastolic BP 90–99 mm Hg. It is concluded that in this population, the hypertension prevalence by epidemiological method is overestimated by 12.2% against clinical hypertension prevalence.