Background: Calcium is the most common cation in the human body. An abnormal distribution of intracellular and extracellular ionized Ca plays a significant role in the formation of arterial hypertension. The purpose of the study is to analyze the fractional composition of calcium in blood serum and urinary calcium excretion in patients with hypertension, as well as to identify the features of the distribution of these. Material and methods: The study included 80 patients. The population of the study consisted of 60 patients with various degrees of hypertension (38 women and 22 men) aged from 65 to 74 years old and the control group composed of 20 patients (12 men and 8 women) in the same age group without signs of hypertension. The patients with clinically expressed coronary heart disease requiring specific therapy, heart defects, impaired liver function and impaired kidney function were excluded from this study. Patients were divided into three groups, according to the World Health Organization (WHO) classification of arterial hypertension. Indicators of calcium concentration in blood and urine were determined using test kits for determining calcium with glyoxal bis-2 hydroxyanil from LACHEMA. To determine the ionized calcium, a standard technique of ion-selective electrode was used. Results and conclusion:1. In patients with arterial hypertension, a redistribution of the calcium pool in the blood is noted due to a decrease in the concentration of ionized calcium and an increase in the bound calcium, depending on the severity of the disease.2. An increase in urinary calcium excretion in patients with arterial hypertension is characteristic of moderate and severe forms of arterial hypertension, which given the age of patients, may be one of the causes of osteoporosis. 3. The increase in the level of intracellular calcium with the progression of arterial hypertension is an example of pathophysiological reactions that occur at the body level, the result of which can be not only banal muscle constriction but also a violation of the synthesis and production of biologically active substances that regulate blood pressure.