When interpreting home blood pressure (BP) measurements in hypertensive patients, differences between clinic and home BP should be noted. To investigate the differences between clinic and morning home BP in hypertensive patients, we analyzed clinic systolic BP (CSBP) and morning home systolic BP (MHSBP) data from the large-scale observational HONEST (Home BP measurement with Olmesartan Naive patients to Establish Standard Target blood pressure) study (n=21 340), using BP measurements obtained before starting olmesartan administration. We generated Bland-Altman plots, with the horizontal axis representing mean CSBP and MHSBP ([CSBP+MHSBP]/2) and the vertical axis representing the difference between CSBP and MHSBP (CSBP-MHSBP). We also did simulation experiments to explore factors affecting the results of the Bland-Altman plots. The difference between CSBP and MHSBP increased as the mean of the two values increased, and when the mean of CSBP and MHSBP was close to 140 mm Hg, the difference was theoretically 0 in average, although large interindividual BP variability existed in this BP range. Results were unaffected by factors such as previous antihypertensive treatment, age and concomitant diabetes or chronic kidney disease. Bland-Altman plots generated from simulated data of normal distribution showed that the slope of the regression line sloped upward, consistent with the results of the HONEST study, when the interindividual BP variability of MHSBP was less than that of CSBP. In conclusion, differences between mean CSBP and MHSBP may be caused by large interindividual variability in CSBP. Therefore, the differences between MHSBP and CSBP may vary between patient groups, which should be noted in the management of hypertension.