There are so many reports in the literature about MRI findings of multiple sclerosis. Multiple sclerosis usually presents with disseminated plaques of demyelination. But in some cases, it presents with a large, solitary lesion with extensive edema and mass effect that mimic intracranial neoplasms. This condition results in a diagnostic confusion for radiologists. In these cases, the differentiation between multiple sclerosis and neoplastic lesions is almost impossible on conventional MRI sequences. If newer MRI sequences such as perfusion and diffusion weighted imaging are not performed, unnecessary resection and radiotherapy may be an important problem for these cases. The purpose of this case report is to reveal the significance of perfusion weighted MRI examinations in differentiating of tumefactive demyelinating lesions from intracranial neoplasms. © 2005 Elsevier Ireland Ltd. All rights reserved.