Detecting cortical demyelination in patients with multiple sclerosis (MS) is difficult. Using magnetic resonance imaging (MRI), ratio maps of T1-weighted and T2-weighted images (T1w/T2w) may be sensitive to cortical myelin levels. In this MRI-histological study, postmortem in situ scans were acquired from six cadavers with MS on a 3 Tesla MRI. Immunocytochemistry was used to correlate myelin status and cortical T1w/T2w measures. The results showed that the T1w/T2w values significantly differed between demyelinated and myelinated cortex (p < 0.001). The T1w/T2w ratio maps may be a relatively simple, clinically feasible method to assess cortical demyelination. This article is protected by copyright. All rights reserved.