Purpose : Primary HyperTension (HT) is the most prevalent cardiovascular disorder worldwide, and has very significant morbidity and mortality. The objective of this study was to investigate in primary hypertensive patients the kinetics of the orthostatic Blood Pressure (BP) during the change from a supine position to a standing position, as well as during the standing position, using the orthostatic test. Patients and methods: This prospective study included a group of 107 primary hypertensive patients (mean age 55.82 ± 11.35 years, with the extremes ranging from 39 to 80 years). Orthostatic systolic BP (Ortho SBP) was recorded for 10 minutes at the rhythm of 3 measurements per minute and compared with the values of supine systolic pre-orthostatic (Preortho SBP). According to the changes in Ortho SBP, three subgroups of primary hypertensive patients were selected as below:Subgroup A: Ortho SBP was higher than mean Preortho SBP by 10 mmHg or more. Subgroup B: Ortho SBP was lower than mean Preortho SBP by 20 mmHg or more. Subgroup C: -20 mmHg < (Ortho SBP – Preortho SBP) < + 10 mmHg.The kinetics of each groups were recorded. Results: Mean Preortho SBP was 150.0 ± 6.2 mmHg, with the extremes ranging from 147 to 163 mmHg. Mean Ortho SBP was 177.5 ±17.3 mmHg, with the extremes ranging from 135 to 220 mmHg, excluding the patients with OH. The prevalence’s of subgroup A, subgroup B, and subgroup C were, respectively, 27.1% (29/107), 15.9% (17/107), and 57.0% (61/107) of which, 69% (20/9), 59% (10/17), and 62.3% (38/61) were women respectively in each sub-group. The kinetics of the Ortho SBP for the 3 subgroups was as the following: In subgroup A, in comparison to Preortho SBP, the mean ortho SBP increases and reaches a maximum value in the first minute of OT. Ortho HT is maintained throughout the 10 minutes duration of test. In subgroup B, SBP decreases during the whole OT. OH is maintained throughout the duration of the OT and in this subgroup 61.7% were women. In subgroup C, the change in SBP is small, maintained between -9.3 and +1.67,Conclusions: hypertensives with very similar supine SBP behavior can exhibit widely different ortho SBP. This has important consequences for both the diagnosis and the treatment of hypertensives. Careful and effective treatment of hypertensives requires careful consideration and assessment of orthostatic BP.Key words: primary arterial hypertension, autonomic nervous system, orthostatic hypertension, orthostatic hypotension.