OBJECTIVE To investigate whether young IDDM patients develop central nervous dysfunction and to establish a possible relationship with various disease parameters. METHODS Thirty-two patients, aged 13.5 +/- 2 years, with disease duration of 6 +/- 2.6 years and age of onset of 7.7 +/- 3.2 years (group 1), and 21 patients with short-term disease, age 9.7 +/- 3.5 years, duration of disease < 2 years and age of onset of 9.4 +/- 3.3 years (group 2) were compared with age- and sex-matched control subjects. Exclusion criteria were clinical signs of neuropathy, retinopathy, nephropathy, or hearing impairment. Neurophysiological studies included auditory and visually evoked potentials (EPs). RESULTS Patients in group 1 revealed increased P100 latencies of visually EPs (103.4 +/- 4.5 vs. 96.8 +/- 3.7 ms) and interpeak latencies I-V of auditory EPs (4.16 +/- 0.10 vs. 3.99 +/- 0.09 ms) and had abnormal latencies (values outside 2.5 SD) in 37%. However, short-term patients (group 2) had results within normal limits compared with control subjects. In group 1, longer disease duration and younger age at onset correlated with an increase of P100 latency (P < 0.001) and IPL I-V (P < 0.001). Patients with a history of severe hypoglycemic episodes had increased latencies compared with patients without hypoglycemia (P < 0.05). Furthermore, metabolic control during the last 2 years was related to P100 latencies (P < 0.05). CONCLUSIONS EPs noninvasively detect subclinical central nervous system involvement in children and adolescents with IDDM. Most important risk factors are duration of disease and frequency of severe hypoglycemia.