Rare forms of demyelinating disease such as Balò's concentric sclerosis or Schilder's disease may simulate brain tumors, both clinically and on the computed tomography (CT) and magnetic resonance imaging (MRI). Even the histopathological diagnosis after a biopsy is not entirely reliable. We report three cases of pseudotumoral demyelinating disorders having required a stereotaxic biopsy, one of which was erroneously diagnosed as a malignant astrocytoma. We describe MRI especially the intense contrast enhancement with ill-defined margins, and the mild mass effect. We then detail the histopathological processes upon which differential diagnosis with a tumor can be based.