Objective Natalizumab is a new and efficient treatment for multiple sclerosis (MS). The risk of developing progressive multifocal leukoencephalopathy (PML) during the use of this drug has created the need for better comprehension of JC virus (JCV) infection. The objective of the present study was to assess the prevalence of JCV-DNA in Brazilian patients using natalizumab. Method Qualitative detection of the JCV...