To evaluate the presence of electrophysiological abnormalities in the visual function of young persons with diabetes, visual evoked potentials were recorded, in basal conditions and after photostress, in 30 patients with newly diagnosed insulin-dependent diabetes mellitus. Their mean age was 17.6 years (3.6 SD), and their glycosated haemoglobin (HbA1c) was 9.4% (1.6 SD). Thirty healthy age- and sex-matched individuals were evaluated as the control group. This study showed that the P100 latency was significantly delayed in patients with diabetes compared with the control group (p<0.01), while the N75 to P100 amplitude was similar in both groups. These measurements were repeated after 6 months, when all participants with diabetes had achieved good metabolic control (HbA1c 7.2% [1.5 SD]). At this second evaluation a complete normalisation of all parameters was observed. These findings suggest that early functional abnormalities of the optic nerve can be detected at onset of diabetes, and that glycaemic control reverses these abnormalities.