A 45-year-old patient suffering from chronic renal insufficiency developed dermatopolymyositis. Since the patient did not respond to treatment with high doses of prednisone and immunoglobulin, concomitant cyclosporine A was added. Four months later, worsening signs of bilateral pyramidal disorder and an altered state of consciousness appeared. Serial computed tomography (CT) and magnetic resonance imaging (MRI) revealed multiple alterations of the cerebral white matter. Cyclosporine was then discontinued. One month later, exitus occurred. Microscopic examination of the brain showed diffuse tumescence; histological examination revealed perivascular and diffuse lymphomonocyte infiltrations, areas of demyelination, astrocytes with bizarre nuclei, and oligodendrocytes with enlarged nuclei due to hyperchromatic inclusion. Morphological examination confirmed the presence of intranuclear icosahedral viral bodies. Progressive multifocal leukoencephalopathy was diagnosed. The literature contains only one report of an analogous case observed during a course of cyclosporine treatment for Wegener's granulomatosis.