The clinical course and computed tomographic findings in two patients suffering from multiple sclerosis and coincidental gliomatous brain tumor are presented. Both diagnoses were proven by surgical biopsy; autopsy findings of one case are reported as well. Our results demonstrate that a differentiation of both diseases is not possible by computed tomography or by clinical data alone. Surgical biopsy to establish the diagnosis is indicated during the course of suspected multiple sclerosis when computed tomographic alterations and clinical signs of a space-occupying lesion last for some weeks.