The prevalence of resistant hypertension (RHT) still remains unknown. Aim of the study was to investigate in a large cohort of hypertensive patients the prevalence of RHT, and to identify in these patients the secondary forms of arterial hypertension (SH). We enrolled a series of 3685 consecutive hypertensive patients. All patients underwent complete physical examination, laboratory tests, screening for SH. Ambulatory blood pressure monitoring (ABPM) was performed to exclude white-coat hypertension. Further, we investigated for any obstructive sleep apnea syndrome (OSA). Only 232 (5.8%) hypertensive patients fulfilled criteria for RHT. 91 (39%) had a SH; 56 (61%) hypertensive patients had a primary aldosteronism, 22 (24%) had OSA, 7 (7.7%) had a hypercortisolism, and 5 (5.5%) had a renovascular hypertension (RVH). Only one patient had adrenal pheochromocytoma. An accurate definition and investigation into RHT is needed. We recommend ABPM to all patients at diagnosis. Finally, all patients must be screened for SH, such as adrenal hypertension, OSA and RVH, especially those who are apparently resistant to polypharmacological treatment
