"the context of whether the kidney fails acutely or chronically is very relevant to the answer. people can often be born with a malfunctioning kidney, and in cases such as these, the other kidney becomes very much larger to compensate. this person will eventually need another kidney otherwise they will die from not being able to remove toxins from the body, and in particular not being able to excrete potassium. in an acute state, this would be life threatening, and emergency heamodialysis would be only treatment. having said that I cant think of a sitauation where just one kidney would fail, because its much more common for both kidneys to fail. the only situatoin where one kidney would be failing would be as I said if you are born with a defunct one, in which case, renal failure would no the be the presenting complaint, it would be stunted growth." http://answers.yahoo.com/question/index?qid=20080402114054AAkjdVl "Total or nearly total and permanent kidney failure is called ESRD. If a person’s kidneys stop working completely, the body fills with extra water and waste products. This condition is called uremia. Hands or feet may swell. A person will feel tired and weak because the body needs clean blood to function properly. Untreated uremia may lead to seizures or coma and will ultimately result in death. A person whose kidneys stop working completely will need to undergo dialysis or kidney transplantation." http://kidney.niddk.nih.gov/Kudiseases/pubs/yourkidneys/#fail