Hyperkalemia is a common and potentially lethal clinical problem. It may be caused by several drugs, especially those which target the renin-angiotensin--aldosterone system, inability of kidney to excrete potassium, a shift of these ions into the extracellular fluid, or a combination of those mechanisms. It can be also spurious, caused by hemolysis after blood drawing. In the article the conditions associated with hyperkalemia, its diagnosis and the management are reviewed.