Frontotemporal dementia (FTD) is the second most common type of primary degenerative dementia. Some patients present an overlap between Alzheimer's disease (AD) and FTD both in neuropathological and clinical aspects. This may suggest a similar overlap in physiopathology, namely an involvement of mitochondrial DNA (mtDNA) in FTD, as it has been associated to AD. To determine if mtDNA is involved in FTD, we performed a Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) analysis, specific to mtDNA NADH Dehydrogenase subunit 1 (ND1) nucleotides 3337-3340, searching for mutations previously described in Parkinson's and AD patients. We could identify one FTD patient with two mtDNA transitions: one already known (3316 G-to-A) and another unreported (3337 G-to-A). Additionally, mitochondrial respiratory chain complex I activity was reduced in leukocytes of this patient (36% of the control mean activity). To our knowledge, this is the first report of mtDNA variants in FTD patients.