Twenty-five cases of non-insulin-dependent diabetes mellitus in the young were investigated for autonomic dysfunction by simple electrophysiological tests to assess the integrity of the cardiovascular reflexes. The mean age of the group at the onset of symptomatic diabetes mellitus ws 27 +/- 0,7 years, and that at the time of investigation for autonomic dysfunction ws 34 +/- 1,3 years. Nine patients had clinical evidence of peripheral neuropathy, while only 3 of the 25 had symptoms of autonomic neuropathy. Fourteen patients showed an abnormality during one or more tests for autonomic function, and of this group 9 had unequivocal evidence of autonomic neuropathy. Only 3 patients displayed both sympathetic and parasympathetic impairment of autonomic function, being the only patients exhibiting symptoms of autonomic impairment. The remaining patients with autonomic dysfunction showed only parasympathetic dysfunction. This study demonstrates that subclinical autonomic neuropathy is not an uncommon occurrence in cases of non-insulin-dependent diabetes mellitus in the young and emphasizes the need for a greater awareness of this complication.