Leber's hereditary optic neuropathy (LHON) is a genetic disease leading to the loss of central vision and optic nerve atrophy. The existence of occasional cases of LHON patients developing a Multiple Sclerosis (MS)-like illness and the hypothesis that mtDNA variants may be involved in MS suggest the possibility of some common molecular mechanisms linking the two diseases. We have pursued a comparative proteomics approach on cerebrospinal fluid (CSF) samples from LHON and MS patients, as well as healthy donors by employing 2-DE gel separations coupled to MALDI-TOF-MS and nLC-MS/MS investigations. 7 protein spots showed significant differential distribution among the three groups. Both CSF of LHON or MS patients are characterized by lower level of transthyretin dimer adduct while a specific up regulation of Apo A-IV was detected in LHON CSF.