Objective: Current European guidelines recommend ambulatory blood pressure (BP) monitoring (ABPM) for the diagnosis and follow-up of patients with known or suspected hypertension. Thus in 2021 the Hungarian Society of Hypertension initiated a nationwide registry in order to evaluate ABPM indications and patient characteristics. Design and method: This is an ongoing, multicenter, open-label, observational study. Data collection to an electronic case report form is performed by GPs, internists and cardiologists. For ABPM measurements Meditech-ABPM-06 monitors are used. Data of the current analysis were collected between 21.02.2021-5.10.2022. 15 835 ABPMs were performed; due to missing data or protocol deviation 1018 patients were excluded from the analysis. Results: 10 212 patients were known and treated hypertensives (HT), and 4 571 were newly diagnosed or suspected hypertensives (nHT) (69% and 31%, respectively; females: 51.1%, males 48.9%). 76% of the nHTs were untreated. They were 12 years younger than HT patients (46.7 ± 13.9 and 59.1 ± 13.9 years old, respectively p<0.001). Besides high BP, other atherosclerotic risk factors and comorbidities were less frequent in nHT patients than in HT patients: dyslipidemia was known only in 11.8% vs. 28.7%, obesity (BMI > 30 kg/m2) in 32.2% vs. 40.3%, diabetes 2.7% vs. 13.1%, coronary heart disease in 0.8% vs. 9.6% of patients, respectively. In the HT group compared to the nHT group there were more cerebrovascular (3.3% vs 0.8%, p<0.001) and peripheral arterial diseases (1.8% vs 0.4%, p<0.001). In both groups the main indication of ABPM was high (62%) or labile (39.5%) home BP values. More ABPMs were performed in the nHT group because of the suspicion of white-coat- (19.2% vs. 9.0%, p<0.001), or masked hypertension (3.9% vs. 0.9%, p<0.001). Hypertension was diagnosed by the largest percentage in patients with suspected resistant hypertension (83%) and by the lowest percentage with suspected nocturnal hypertension (57%). Conclusions: The major indications for ABPM are the high or labile home BP values. Among nHTs suspected white coat hypertension is the third most important indication for ABPM, while in HT patients the follow up of therapies. Additional risk factors and comorbidities are less known in nHTs.