Hyperkalemia is a frequently met electrolytic disorder in clinical practice. Blood potassium concentration is primarily under the control of cellular transfer, driven either by the acid basic equilibrium, the action of catecholamines and insulin, and secondarily by the kidney. In the majority of cases, hyperkaliemia is due to renal failure, together with the effect of drugs. The clinical symptoms, particularly cardiac manifestations, of hyperkaliemia can be serious, and this is why the identification of its cause and its treatment are of the utmost importance. The diagnostic strategy rests on a detailed history taking, centered on the drug therapies. The transtubular gradient of potassium can be useful, when there is a suspicion of hypoaldosteronism.