Objective To examine factors affecting systolic blood pressure (SBP) variability during a single clinic visit, in treated hypertensive patients. Methods Hypertensive patients were recruited to this observational study. Blood pressure was measured using an automated blood pressure monitor when each patient arrived at the outpatient clinic and again when they saw the physician. Mean SBP and SBP variability during a single clinic visit were calculated. The cardio–ankle vascular index (CAVI), as a marker of arterial stiffness, was also measured. Results A total of 57 treated hypertensive patients (mean age 71 years) were included in the study. The mean SBP was positively correlated with age ( r = 0.457), while SBP variability was positively correlated with age ( r = 0.383), CAVI ( r = 0.330), and glycosylated haemoglobin ( r = 0.345) and triglyceride levels (r = 0.299). Conclusion Variability in SBP during a single clinic visit showed better correlations with arterial stiffness and risk factors for atherosclerosis than did mean SBP. Large SBP variability during a single clinic visit may reflect progression of atherosclerosis, in treated hypertensive patients.