OBJECTIVE: This article describes the rationale and methodology for the monitoring of ambulatory blood pressure and arterial compliance in hypertensive patients aged 80 years and above. This is a side project of the Hypertension in the Very Elderly Trial. METHODS: The hypertension in the Very Elderly Trial is a multicentre, double-blind, randomized, placebo-controlled trial aiming to investigate the effect of active treatment on cardiovascular and other outcomes in hypertensive patients aged 80 years or more. Patients are randomized to placebo or active treatment starting with the diuretic indapamide and adding the angiotensin-converting enzyme inhibitor perindopril if required. This study has completed a pilot trial and the main trial is now underway. Six hundred patients will have two ABPM recordings, the first at baseline and the second a year after randomization. Arterial compliance is measured using the Q wave (electrocardiogram) to Korotkoff diastole sound interval. RESULTS: Baseline characteristics for the first 50 patients recruited are presented. CONCLUSION: This side project will allow the investigation of 24-h ambulatory measures of blood pressure and arterial compliance as predictors of cerebrovascular and cardiovascular events in the very elderly. The project will also allow the investigation of the blood pressure and vascular compliance profiles in the very elderly and their changes with posture. The association between these measurements and mortality and morbidity in this age group will be addressed.