Thirty-seven diabetics with symptoms and clinical features suggestive of autonomic neuropathy were followed up for 33 months. Of the twenty with abnormal Valsalva or handgrip tests initially, ten (50%) died. There were no other features at presentation that differentiated those who subsequently died from those who survived. The causes of death were renal failure (six patients), cerebrovascular accident (two patients), hypoglycaemic coma (one patient), and "sudden death" (one patient). Of the survivors whose autonomic-function tests were repeated 18 months to 2 years later, five had new or worsening symptoms of autonomic neuropathy with corresponding deterioration of their autonomic-function tests; while two, with initially normal tests, had improved symptomatically. It is concluded that in diabetics with the clinical features of autonomic neuropathy simple autonomic-function tests give a good guide to prognosis, and that abnormal tests are associated with a high mortality.