In a patient with kidney (renal) failure, the kidneys are unable to remove wastes and excess fluid from the body. This often occurs as a complication of other illnesses. Usually, more than one factor is present that contributes to its development.

Kidney failure can occur suddenly (acute) or over a long time (chronic). If kidney failure is severe enough, a dialysis machine may be required to replace the function of the kidneys.

When kidney failure is acute, treatment of the underlying illness usually enables the kidneys to start working again. However, if damage to the patient's kidneys has been present/worsening over a long time (chronic renal failure), the kidneys may not get better and life-long dialysis may be required.