The surge in blood pressure (BP) upon rising after waking in the morning has been associated with increased risk of target organ damage and cardiovascular events. The reproducibility of this phenomenon within the same 24-h period was tested in subjects with a siesta during ambulatory BP monitoring by assessing the morning surge (MS) vs. the evening surge (ES) after siesta. Ambulatory BP recordings with reported siesta from hypertensive subjects were analyzed. MS and ES were assessed using four different definitions. The intraindividual reproducibility was assessed using the standard deviation of differences between MS and ES, the concordance correlation coefficient, the coefficient of variation and the agreement between MS and ES in detecting "surgers" among hypertensive subjects (top quartile of the BP surge distribution). A total of 562 ambulatory recordings were analyzed (476 subjects, mean age 54.9+/-13.2 [SD] years, treated 47%). Average MS (16.3/14.4 mmHg, systolic/diastolic) was higher than ES (13.3/12.1 mmHg, p<0.001) due to higher post-rising BP in the morning (p<0.01). The intraindividual reproducibility was rather poor, with no clear differences among different definitions. However, there was about 70% agreement between MS and ES in the detection of "surgers" (systolic and diastolic, kappa statistic 0.18). These data suggest that, although the intraindividual reproducibility of the BP surge within the same 24-h period is rather poor, about 70% of the "morning surgers" were also "evening surgers." Thus, the BP surge might be an inherent pathophysiological characteristic of the BP behavior of an individual and deserves further investigation.