Multiple sclerosis is the most frequent demyelinating disease in adults. It is characterized by demyelination, inXammation, gliosis and a variable loss of axons. Clinically and histologically, it shares features with other demyelinating and/or inXammatory CNS diseases. Diagnosis of an inXammatory demyelinating disease can be challenging, especially in small biopsy specimens. Here, we summarize the histological hallmarks and most important neuropathological diVerential diagnoses of early MS, and provide practical guidelines for the diagnosis of inXammatory demyelinating diseases.