We studied 21 cases of pathologically confirmed tumefactive demyelinating lesions and reviewed the spectrum of tumefactive demyelinating lesions in the literature. Radiological features and clinical data were reviewed to characterize the lesions as consistent with a known demyelinating disease, most notably multiple sclerosis. Atypical clinical or radiological features (other than tumefaction) were noted. Most lesions were part of a clinical and/or radiological picture consistent with multiple sclerosis. No case strongly suggestive of variants or related diseases, such as Schilder's disease or Balo's concentric sclerosis, were found. There was one case suggestive of acute disseminated encephalomyelitis. Features which help distinguish the lesions from tumour are discussed.