The increased incidence of hypertension and cardiovascular diseases in industrialized societies is associated with sodium-rich and potassium-poor diet. Potassium is the main intracellular cation of the system and is involved in formation of the rest and the action potential of nerve cells. Additionally, this element participates in maintaining the water and acid-base balance. The ability of the kidneys to retain potassium is low what is the cause of hypokalaemia in persons who consume small quantities of this element. Hypokalaemia occurs more often than hyperkalaemia. The incidence of hypokalaemia is varied and it ranges 14–20%, depending on the studied population. Patients suffering from diseases such as hypertension, heart failure, arrhythmia, diabetes and kidney failure, as well as people at risk of stroke, require special attention and monitoring in order to prevent hypokalaemia. Disturbances in potassium metabolism lead to life-threatening complications. Hypokalaemia may cause cardiac arrhythmia. In the consequence, it may cause to ventricular fibrillation. In contrast, hyperkalaemia may results in conduction disturbances, bradycardia and even asystolia. The results of numerous studies proved a protective effect of normal levels of potassium on the cardiovascular diseases, thereby reducing the risk of death. One of the main ways of prevention and good control of potassium disorders is a lifestyle change and, above all, a proper diet. In patients with cardiovascular diseases, a control of serum concentration of potassium seems to be justified. The recommended daily intake of potassium should be primarily achieved through a proper diet. In patients receiving diuretics, that lead to hypokalaemia, it is advisable to use potassium supplementation.