Purpose: To assess changes of retinal ganglion cells (RGCs) and visual pathways’ function in patients with Leber's hereditary optic neuropathy (LHON) during 12 months of follow-up of the chronic phase. Design: Retrospective case series. Participants: Twenty-two patients with LHON (mean age, 36.3±9.3 years) in the “chronic phase” of the disease, providing 42 eyes (LHON group) with different pathogenic mitochondrial DNA mutations (group 11778: 21 eyes; group 3460: 4 eyes; group 14484: 13 eyes; and group 14568: 4 eyes) were enrolled. Twenty-five age-similar healthy participants, providing 25 eyes, served as controls. Methods: Pattern electroretinogram (PERG) and visual evoked potentials (VEP), in response to 60ʹ and 15ʹ checks visual stimuli, were recorded at baseline in all subjects and after 6 and 12 months of follow-up in patients with LHON. At baseline, in all LHON eyes for each PERG and VEP parameter (amplitude and implicit time), the 95% confidence limit (CL) of test–retest variability was calculated. The PERG and VEP mean values observed in LHON eyes were compared (1-way analysis of variance [ANOVA]) with those of controls. During the follow-up, the PERG and VEP differences observed with respect to baseline were evaluated by ANOVA. Main Outcome Measures: Changes of individual and mean absolute values of 60ʹ and 15ʹ PERG amplitude and VEP amplitude and implicit time at each time point compared with baseline values in the LHON group. Results: At baseline, mean values of PERG and VEP parameters detected in the LHON group were significantly (P <0.01) different with respect to control values. In the LHON group, at 6 and 12 months of follow-up, the majority of eyes showed unmodified (within 95% CL) PERG and VEP values, and mean absolute values of these measures were not significantly (P > 0.01) different from baseline values. Conclusions: In our untreated patients with chronic LHON, with different specific pathogenic mutations, RGCs and visual pathways function were not significantly modified during 12 months of follow-up. This should be considered in the disease natural history when attempts for treatments are proposed in chronic LHON.