The prognosis for diabetics with autonomic neuropathy is little known. We therefore studied the progress of young insulin-dependent diabetics, first identified as having abnormal autonomic function 10-15 years ago. We have shown that the mortality of diabetics with symptomatic autonomic neuropathy is increased, but is less than previously reported. Mortality in asymptomatic diabetics with an isolated abnormality in autonomic function tests is not increased. The heart rate variability declines at 1.02 +/- 0.47 (SD) per annum in diabetics with an initially normal heart rate variability. While symptoms of autonomic neuropathy do not usually remit even over a decade, they do not commonly progress. Three groups of young insulin-dependent diabetics had heart rate variability tested between 1972 and 1977 and have been reviewed 10-15 years later. Group A (n = 49) had symptomatic autonomic neuropathy and an abnormal heart rate variability (less than 12), Group B (n = 24) were asymptomatic yet had an abnormal heart rate variability and Group C (n = 38) were asymptomatic and had a normal heart rate variability (16-26). The 10-year survival in Group A (73.4 per cent) was less (P less than 0.05) than in Groups B (91.7 per cent) or C (89.5 per cent) which did not differ from each other. The 18 Group A deaths were due predominantly to renal failure (n = 4), myocardial infarction in patients with nephropathy (n = 3) and sudden unexpected death (n = 3). The chief symptoms of autonomic neuropathy--diarrhoea, postural hypotension and gustatory sweating, were very persistent but did not necessarily deteriorate or become disabling in the majority of patients. The development of autonomic symptoms in asymptomatic patients with abnormal heart rate variability was uncommon over a decade.