Purpose The purpose of the study was to present results from a national Dutch cohort of patients with Leber's Hereditary Optic Neuropathy (LHON) treated with idebenone. Methods The multicentre, open-label, retrospective evaluation of the long-term outcome of idebenone treatment of Dutch LHON patients on visual function and on thickness of the retinal ganglion cell layer. Patients included in the analysis had a confirmed mutation in their mitochondrial DNA encoding either of the seven subunits of complex I, had a reported loss of vision in at least one eye and had a follow-up of more than 6 months after their treatment was started. Control visits involved routine clinical examinations of visual function and retinal structure at (1) the start of treatment, (2) nadir (time of lowest visual acuity), (3) the time of recovery (if any), (4) the time of termination of treatment and (5) more than 6 months after termination of the treatment. Results Data from 72 patients were analysed. Treatment duration was 23.8 +/- 14.4 (mean +/- SD) months. A positive response, that is either a clinically relevant recovery (CRR) or a clinically relevant stabilization (CRS), occurred in 53% and 11% of the patients, respectively. The magnitude of CRR was 0.41 +/- 1.54 logMAR. CRR of visual acuity is associated with recovery of colour discrimination. The thickness of both the ganglion cell complex (GCC) and the retinal nerve fibre layer (RNFL) is irreversibly reduced. Conclusion Our results confirm that idebenone may help to restore or maintain visual function. Whether this effect will persist is still unknown. Thinning of retinal neural tissue appears to be permanent.