Hypokalemia is frequently encountered in clinical practice. It can be due to either potassium deficiency (inadequate potassium intake or excessive potassium loss) or to net potassium shifts from the extracellular to the intracellular compartment. Inadequate dietary intake of potassium alone rarely causes hypokalemia since kidney is able to lower potassium excretion below 15 mmol per day. Hypokalemia due to excessive potassium loss can be due to renal or extrarenal losses. It is not necessary to wait for a timed urine collection for potassium to determine the etiology of hypokalemia. Measurement of spot urine for potassium and creatinine as well as evaluation of acid-base status can be used as an initial step in the diagnosis of hypokalemia. Subsequent evaluations such as measurement of spot urinary chloride, blood pressure, serum aldosterone, renin and cortisol levels may be needed in certain circumstances.