Amyotrophic lateral Sclerosis (ALS) is characterized by progressive degeneration of spinal cord motor neurons. To address the role of axonal pathology in ALS, we generated a YFP,G93A-SOD1 reporter mice. Our goal in this study is to evaluate if presymptomatic alterations in MRI water diffusion in the YFP,G93A-SOD1 mice are related to alterations in axonal connectivity by histological methods. Results showed presymptomatic changes in diffusion parameters are associated to specific structural changes in axonal population. The use of this new animal model will help us to understand the structural basis of changes in water diffusion in ALS.