Acute renal failure, ACR, is diagnosed in approximately 5% of hospitalized patients. Most frequent causes are altered renal blood flow due to low volumen, low renal perfussion or inaduate intrarrenal distribution and obstruction of the urinary tract. ACR diagnosis begins with a good clinical history and an adequate physical examination complemented by urinary indexes (sodium excretion and osmolarity), urine analysis and renal echography. Treatment includes adequate recuperation of renal flow, use of diuretics, hydroelectrolitic balance and nutritional support. Renal dyalisis should be considered in presence of toxic uremia or severe hypercalcemia (>6.5 mEq/l), metabolic acidosis or severe volumen overcharge.