Objective: The goal of the TREAT study is to evaluate the prevalence of apparent treatment-resistant hypertension (aRHT) in a Belgian setting and to evaluate which determining factor of pseudo-resistant hypertension contributes the most to this prevalence: white coat hypertension (WCH), underdosing of adequate drugs or poor adherence to prescribed medicines. Design and method: TREAT is a single-visit, multicentric, non-interventional, cross-sectional survey. Inclusion criteria were the following: patients over 18 years old receiving 3 or more antihypertensive molecules and referred to specialized hospital centres for aRHT. The data were collected according to the patient’s medical records. Self-reported adherence to antihypertensive treatment was collected and a Hill-bone medication adherence scale was also proposed. Results: A total of 232 patients were included. Mean anti-hypertensive treatment duration was 10.6(±9.1) years. Patients were treated with a mean of 3.8(±1.1) antihypertensive molecules and 2.8(±1.1) antihypertensive pills. Only 48.5% of the aRHT patients were treated with the triple therapy recommended by the 2023 ESH hypertension guidelines (i.e. renin-angiotensin-aldosterone system inhibitor (RAASi), calcium channel blocker (CCB) and diuretic), and only 29.1% of patients were treated with the maximal recommended dose. Inadequate dosing was mostly present with diuretics, only 60% of patients was treated with at least half the maximum dose of a diuretic. WCH was present in 11% of patients in whose ambulatory BP measurements were available in records (n=136). Therapeutic adherence was self-reported as poor or moderate in 17.6% of patients (n=41). The Hill-bone medication adherence scale (n=140, 60.4%) showed a mean score of 12(±4.2) (good adherence). In this cohort, 31.8% of patients seemed to have true resistant hypertension. Conclusions: Among patients referred to specialized centres for aRHT, about 2/3 of patients have in reality pseudo-resistant hypertension. Whereas WCH and poor adherence seems to be limited in our dataset, many patients were polymedicated with non-recommended combinations of antihypertensive molecules in 1 out of 2 patients, with inadequate dosing in 2 out of 3 patients. Pseudo-resistant hypertension seems in our cohort to be mainly related to under-use of triple combination therapy and most likely also due to underdosing.