Arterial stiffening may be both the cause and consequence of an increase in blood pressure but the blood pressure components implicated in the inter-relationship may differ. The blood pressure component caused by stiffening is pulse pressure (PP). By contrast, passive stiffening resulting from distension of the arterial wall would be expected to relate most closely to mean arterial blood pressure (MAP) at the time of measurement and stiffening related to structural change to relate to longer term MAP and/or pulse pressure (PP). The objective of the present study was to examine the relation between arterial stiffness as measured by carotid-femoral pulse wave velocity (PWV) and components of blood pressure (MAP and PP) at the time of the measurement of PWV (PWV BP) and over a 24 hour period in children with hypertension and chronic kidney disease (CKD). Children (n=45, 12 female, 27 with CKD, 11 with hypertension, 7 controls) were aged 6–17 years with mean±SD blood pressure 113±17/62±15 mmHg. PWV was measured by ECG referenced carotid-femoral tonometry (SphygmoCor system, Atcor Medical, Australia). PWV was more closely correlated with MAP than with PP (R=0.38, P<0.01 and R=0.26, P= 0.08 for 24h MAP and PP respectively) and more closely correlated with 24h MAP than with day-time, night-time or clinic MAP (R=0.26, 0.20 and 0.29 respectively). In children with CKD and hypertension, PWV is most closely associated with 24h MAP and likely to be secondary to increased MAP.