Recent studies have linked autoimmunity to nervous tissue structures and diabetic autonomic neuropathy. To evaluate prospectively the early stage of type 1 diabetes and the natural history of this association, we monitored the autonomic function and the presence of autoantibodies (Ab) to sympathetic and parasympathetic nervous structures in a cohort of 92 diabetic adolescent patients, recruited and followed-up after 40+/-3 months. The presence of circulating Ab and their ability to activate complement was also assessed using a human adrenergic neuroblastoma cell line, and the effect of patients' sera on these cells was evaluated by different methods assessing cytotoxic effects and apoptosis. Thirty-nine percent of the Ab-positive patients had one abnormal test (p=0.07 vs. Ab-negative patients). Serum from four patients positive for anti-cervical ganglia Ab showed positive staining of neuroblastoma cells and displayed ability to activate complement. Serum from two adolescent patients with anti-cervical ganglia and anti-neuroblastoma cells Ab, induced cytotoxic effects and damaged the plasma membrane of the neuroblastoma cells. Moreover, sera from two adult patients with overt autonomic neuropathy, used as positive controls, induced apoptosis of these cells, assessed by TUNEL. Our data indicate that symptomatic autonomic neuropathy is not characteristic of young diabetic patients, but that autoantibodies to autonomic structures are present and persist in the first 20 years of disease, possibly associated with subtle autonomic dysfunction and cytotoxic effect on sympathetic cells.