Potassium disorders are the most common electrolyte abnormality in clinical practice. Hypokalemia is usually well tolerated in otherwise healthy people, but it can be life threatening when severe. Even mild or moderate hypokalemia increases mortality and morbidity in patients with cardiovascular disease. Hypokalemia is the result of an abrupt shift of potassium from the extra-cellular compartment into cells or more frequently the result of potassium depletion by abnormal losses (digestive or kidney). Medication (diuretics) is the most common cause of hypokalemia. In some cases the diagnosis is not readily apparent. In this setting, measurement of an urinary potassium excretion and assessment of acid-base balance are often helpful. When hypokalemia is identified, the disorder should be treated by treating the underlying cause.