X-linked adrenoleukodystrophy is a neurometabolic disorder caused by inactivation of the peroxisomal ABCD1 transporter of very long-chain fatty acids. In mice, ABCD1 loss causes late onset axonal degeneration in the spinal cord in association with locomotor disability resembling the most common phenotype in patients, adrenomyeloneuropathy. Increasing evidence indicates that oxidative stress and bioenergetic failure play major roles in the pathogenesis of X-linked adrenoleukodystrophy. In this study, we aimed to evaluate whether mitochondrial biogenesis is affected in X-linked adrenoleukodystrophy. We demonstrated that Abcd1 null mice show reduced mitochondrial DNA concomitant with downregulation of mitochondrial biogenesis pathway driven by PGC-1α/PPARγ and reduced expression of mitochondrial proteins cytochrome c, NDUFB8 and VDAC. Moreover, we show that the oral administration of pioglitazone, an agonist of PPARγ, restored mitochondrial content and expression of master regulators of biogenesis, neutralized oxidative damage to proteins and DNA, and reversed bioenergetic failure in terms of ATP levels, NAD+/NADH ratios, pyruvate kinase and glutathione reductase activities. Most importantly, the treatment halted locomotor disability and axonal damage in X-linked adrenoleukodystrophy mice. These results lend support to the use of pioglitazone in clinical trials with patients with adrenomyeloneuropathy and reveal novel molecular mechanisms of action of pioglitazone in neurodegeneration. Future studies should address the effects of this anti-diabetic drug on other axonopathies in which oxidative stress and mitochondrial dysfunction are contributing factors. ; This work was supported by grants from the European Commission [FP7-241622], the European Leukodystrophy Association [ELA2009-036C5, ELA2008-040C4], the Spanish Institute for Health Carlos III [FIS PI11/01043], the Autonomous Government of Catalonia [2009SGR85 to A.P.], the Spanish Institute for Health Carlos III [Miguel Servet program CP11/ 00080 to S.F.], the COST action [BM0604 to A.P.]. S.F. was a fellow of the European Leukodystrophy Association [ELA 2010- 020F1]. L.M. is a fellow of the Spanish Ministry of Education [FPU program: AP2008-03728]. J.G. was a fellow of IDIBELL. The studies conducted at the Experimental Medicine Department were supported in part by R +D grants from the Spanish Ministry of Science and Innovation [BFU2009-11879/BFI], the Spanish Ministry of Health [PI081843], the Autonomous Government of Catalonia [2009SGR735], the ‘La Caixa’ Foundation and COST B35 Action of the European Union. The CIBER on Rare Diseases (CIBERER) and the CIBER on Neurodegenerative Diseases (CIBERNED) are initiatives of the ISCIII.