Diuretics are agents commonly used in diseases characterized by excess extracellular fluid, including chronic kidney disease, the nephrotic syndrome, cirrhosis and heart failure. Multiple diuretic classes, including thiazide-type diuretics, loop diuretics and K(+)-sparing diuretics, are used to treat patients with these diseases, either individually or as combination therapies. An understanding of what determines a patient's response to a diuretic is a prerequisite to the correct use of these drugs. The response of patients with these diseases to diuretics, which is related to the dose, is best described by a sigmoid curve whose contour can become distorted by any of the several sodium-retaining states that are directly or indirectly associated with renal disease. Diuretic actions are of considerable importance to patients who have renal disease, as their effective use assists in extracellular fluid volume control, reducing excretion of protein in urine and lessening the risk of developing hyperkalemia. Diuretic-related adverse events that involve the uric acid, Na(+) and K(+) axes are not uncommon; therefore the clinician must be vigilant in looking for biochemical disturbances. As a result of diuretic-related adverse events, clinicians must be resourceful in the dose amount and frequency of dosing.