Objectives: Mechanisms underlying the circadian profile of cardiovascular events (CE) are not totally understood. Whether circadian changes in arterial stiffness (AS) could be related to the circadian profile of CE remains to be investigated. As yet, there is no accepted way to measure circadian profiles or nocturnal-related and/or morning-related changes in cardiovascular variables. The aim of this study was to characterize the circadian pattern and day-night and night-day changes of AS in untreated hypertensive (HG) and healthy subjects (NG), using a recently developed non-symmetrical six-parameter double-logistic model. Methods: Seven hypertensive and seven normotensive subjects underwent 24 hour ambulatory recordings of blood pressure (BP), heart rate (HR) and aorto-brachial pulse transit time (PTTAB) and pulse transit velocity index (PTVAB). PTTAB and PTVAB are inversely and directly related to AS, respectively. The circadian profile and transitional periods (day-night and night-day) were analyzed using a model described by a six-parameter double logistic equation. Conclusions: The model was adequate to characterize the circadian pattern of AS. We provide the first evidence that AS in humans follows an asymmetric circadian pattern and that this differs between NG and HG. In both NG and HG, AS had a circadian profile, with the highest levels in the night. HG showed larger levels of AS, larger BP variations and rate of change and minor changes in AS during transitional periods.