Objectives To elucidate the clinical significance of differences between home- and clinic-measured systolic blood pressure (SBP) in patients with treated hypertension, and to assess the correlations between SBPs and arterial stiffness. Methods Patients with treated hypertension measured their blood pressure (BP) themselves once, at home, in the morning (<1 h after awakening) using an automated oscillometric sphygmomanometer. Clinic BP was measured once, at an outpatient clinic on the same day, using a similar instrument. Arterial stiffness was measured by cardio–ankle vascular index (CAVI). Differences between home and clinic SBPs, and the correlations between CAVI and home SBP, clinic SBP, and the difference between home and clinic SBPs, were analysed. Results Seventy-six patients with treated hypertension (mean age, 71 years) were evaluated. There was no statistically significant difference between home and clinic SBP (mean ± SD 132 ± 14 and 133 ± 16 mmHg, respectively). Home SBP showed no correlation with CAVI, whereas clinic SBP showed a weak correlation. The difference between the home and clinic SBP showed a stronger correlation with CAVI, and was statistically significant. Conclusions The difference between home- and clinic-measured SBP showed a better correlation with arterial stiffness than did either home or clinic SBP alone.