Magnetic resonance imaging (MRI) has improved the diagnosis of several pathological entities of the brain. MRI especially has been credited with distinguishing demyelinating diseases of the central nervous system from other diseases. The presence of a mass effect in a demyelinating disorder, however, makes difficult the distinction between tumor and a demyelinating disease. We report a case of a demyelinating disorder simulating an infiltrating glioma of the corpus callosum on MRI scan, resulting in surgical intervention. To our knowledge, this is the first case to be reported with MRI and documented pathological findings.