The present investigation was aimed at determining the prevalence and the blood pressure (BP) profile of isolated ambulatory hypertension, defined as an elevated ambulatory BP with normal office blood pressure, in a series of 1488 consecutive outpatients referred for routine clinical evaluation of suspected or established arterial hypertension. All patients underwent both office BP (OBP) measurement by a physician and 24-h ambulatory blood pressure monitoring (ABPM). Using OBP values (cutoff for diagnosis of hypertension >/=140/90 mmHg) and daytime ABPM (cutoff for diagnosis of hypertension >/=135/85 mmHg), patients were classified into eight subgroups. In the whole series we found that, independent of treatment status, the prevalence of isolated ambulatory hypertension exceeded 10%. More importantly, 45.3% of individuals who presented with normal OBP values, showed elevated BP at ABPM. Night-time BP, 24-h pulse pressure, and BP variability were significantly higher in isolated ambulatory hypertensives than in normotensive or in white-coat hypertensive individuals. Therefore, isolated ambulatory hypertension is characterized by a blood pressure profile that is similar to that observed in sustained hypertension. These findings suggest that isolated ambulatory hypertension is very common and probably the indications for ABPM should be more extensive in outpatients referred to hypertensive centre.