In the 1990s Lange's health declined, with diabetes and kidney disorders. In 2002, doctors diagnosed Lange as having amyloidosis, a rare and incurable blood plasma disorder. He underwent extensive medical treatment for this condition. Although initially told he had only four months to live, Lange defied his doctors' expectations, and remained "optimistic" about his health. He entered hospital in Auckland in mid-July 2005 to undergo nightly peritoneal dialysis in his battle with end-stage kidney failure. On 2 August, he had his lower right leg amputated without a general anaesthetic, as a result of diabetes complications.