OBJECTIVE: To investigate 24-h ambulatory blood pressure measurements (ABPM) as a tool for long-term prediction of future blood pressure (BP) status in high normal and low stage 1 hypertensives. DESIGN, SETTING AND PARTICIPANTS: A total of 165 men from a population screening program with diastolic BP (DBP) 85-94 mmHg and a systolic BP (SBP) < 150 mmHg performed a 24-h ABPM. Ten years later, 120 participants (73%) returned for renewed measurements. MAIN OUTCOME MEASURES: Blood pressure status at 10 years. RESULTS: At the 10-year follow-up, 53% of the participants were classified as hypertensive (HT) (BP > or = 140/90 or taking anti-hypertensive medication) and 47% were classified as normotensive (NT) (BP < 140/90 mmHg). There was no significant baseline differences in office SBP levels between those who were normotensive or hypertensive at follow-up (136/91 versus 138/92 mmHg), whereas both SBP and DBP night-time levels were significantly lower in the future normotensives as compared to the future hypertensives (107/69 versus 112/74 mmHg, P < 0.01). Using recommended normalcy night-time ABP levels of < 120/75 mmHg in addition to office BP (140/90) at baseline, over 85% of the subjects were correctly classified provided they met both clinic and ambulatory night-time criteria for HT and NT classification at baseline. CONCLUSION: The use of ABPM in addition to office BP's in patients with borderline hypertension greatly increases the possibility of identifying those individuals who are at a very small risk of developing future hypertension. This could potentially lead to considerable savings in both patient anxiety, physician time and resource consumption.