OBJECTIVE To compare clinic and 24-h blood pressure levels and profiles in young elderly (aged 65-79 years) and old elderly (aged > or = 80 years) subjects. METHODS A cross-sectional observational study was conducted on 108 ambulant subjects (51 males) aged 65-95 years with no known history of hypertension, recruited from the community (55%) and hospital outpatients (35%) and inpatients (10%). Three clinic blood pressure measurements were taken, followed by 24-h ambulatory blood pressure monitoring and then a further three clinic measurements, the mean of these being defined as the clinic blood pressure. RESULTS Clinic systolic blood pressure was significantly higher in females than males (148 +/- 20 versus 136 +/- 23 mmHg, P = 0.02), but 24-h systolic blood pressure was similar. Mean 24-h and daytime blood pressure levels were significantly lower than clinic blood pressure in females but in males only 24-h systolic blood pressure was lower than the clinic level. In young elderly compared to old elderly females the clinic-daytime ambulatory systolic blood pressure difference was significantly reduced (14 +/- 22 versus 1 +/- 17 mmHg, respectively; P = 0.04). A significant nocturnal systolic/diastolic blood pressure fall was seen in young elderly and old elderly males (9 +/- 12/7 +/- 7 versus 6 +/- 11/7 +/- 8 mmHg) but in females the nocturnal systolic blood pressure fall was inversely related to age (r = -0.32, P = 0.02). CONCLUSIONS The white-coat effect is common in young elderly females, but uncommon in very elderly females and males aged > or = 65 years; a decline in casual blood pressure in the very elderly may partly arise from a reduction in the white-coat effect. Nocturnal blood pressure falls also decline in the very elderly, especially in females.