MRI findings in primary angiitis of the central nervous system (PACNS) are highly variable, ranging from normal to diffusely abnormal. We describe brain and spinal cord abnormalities in patients with PACNS and changes over time, to provide criteria which could be useful for differential diagnosis. We reviewed six patients, with a final diagnosis of PACNS, who underwent serial contrast-enhanced brain and spinal MRI. Follow-up ranged from 12 to 60 months. Brain MRI showed multiple small abnormalities in all patients, giving high signal on T2-weighted images, focal or diffuse, mainly in deep and subcortical white matter; four patients had both supra- and infratentorial lesions. On the initial MRI, in five patients, almost 90% of the abnormal foci showed contrast enhancement. Virchow-Robin perivascular spaces were enlarged and simultaneously enhancing in four patients. Three patients also had spinal cord abnormalities, in the cervical and thoracic segments in two, and exclusively cervical segment in one. Two patients had brain biopsy-proven PACNS; in the remainder, the diagnosis of PACNS was presumptive, considering similarities in clinical and MRI features and MRI follow-up. On MRI, after steroid and immunosuppressive therapy, a significant decrease in the number and size of the abnormalities, enhancing and nonenhancing and of enhancing perivascular spaces was observed. Simultaneous enhancement of brain and spinal cord lesions and of perivascular spaces, at the onset of the disease, which resolves during follow-up, can therefore suggest PACNS.