BACKGROUND: Progressive multifocal leukoencephalopathy (PML) is an opportunistic demyelinating encephalopathy related to JC virus. Its characteristics on conventional brain MRI are well known and are important for the diagnosis. OBJECTIVE: To analyze SWI hypointensities recently described in U-fibers and cortex adjacent to the white matter lesions of PML. METHODS: Prospective study including four patients with an history of definite diagnosis of PML. Clinical data were collected retrospectively. Brain MRI exams were done on a 3T magnet, including FLAIR, T2 GRE sequences and SWI. RESULTS: Four males were included (mean age: 47 years, mean PML duration: 24.2 months). Immunosuppression was related to AIDS (n=2), natalizumab for multiple sclerosis (n=1), B-cell lymphoma treated by chemotherapeutic agents and rituximab (n=1). All patients had SWI hypointensities in cortex and/or U-fibers adjacent to the white matter lesions. QSM always suggested a paramagnetic effect. CONCLUSION: SWI and T2 GRE hypointensities in cortex and U-fibers adjacent to the white matter lesions seem highly prevalent in PML, irrespective of the delay between PML onset and the MRI. QSM data suggest a paramagnetic effect.