Background: Susac syndrome (SuS) is a rare immune-mediated microangiopathy with potential disabling evolution. We aimed to analyze brain microstructural damage through diffusion tensor imaging (DTI) in SuS and determine its association with poor outcomes., Method: CarESS study is a prospective multicenter national cohort study of patients with SuS. Patients included at the principal investigator's center with at least two available brain magnetic resonance imaging (MRI) with DTI were analyzed. Mean diffusivity (MD) and fractional anisotropy (FA) were measured in fibers crossing three regions of interest (ROIs): the corpus callosum as a whole, the genu of the corpus callosum, and the splenium of the corpus callosum. The primary outcome was work resumption., Results: Twenty-two patients (36 (25;42) years, 16 (73%) females) were studied. The triad (i.e., brain, eye, and ear involvement) was complete in 21 (95%) patients. All but one patients received steroids alone or in combination with immunosuppressive drugs (n = 11) and/or IVIg (n = 7). Over a median follow-up of 6 (5;8) years, 15 (68%) patients went back to work. FA and MD were longitudinally measured in 123 DTI MRI accounting for a median of 5.6 [4.2; 7] MRI per patient. Microstructural damages in the corpus callosum as a whole, the genu of the corpus callosum, and the splenium of the corpus callosum increased during follow-up and were significantly associated with the inability to return to work., Conclusion: Brain DTI identified microstructural damage in fibers crossing the corpus callosum that are associated with long-term disability in SuS., Trial Registration: ClinicalTrials.gov portal identifier: NCT01481662 (https://clinicaltrials.gov/ct2/show/NCT01481662?term=caress&draw=2&rank=5)., (© 2024 The Author(s). European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.)