Multiple sclerosis patients examined with perfusion magnetic resonance (MR) imaging techniques have been found to have patterns of abnormal blood flow. These include prolonged mean transit time, a trend toward decreased cerebral blood flow in the area of plaques, and decreased cerebral blood flow and prolonged mean transit time within normal-appearing white matter. Increased cerebral blood flow and volume and decreased mean transit time (compared with the baseline values before the relapse) were found to precede the development of plaques. In addition, susceptibility-weighted imaging utilizing deoxyhemoglobin as the contrast has revealed that venous blood in cerebral veins of multiple sclerosis patients is less deoxygenated compared with healthy controls. All these findings were traditionally interpreted as a sign of local flow disturbances mediated by inflammatory and neurodegenerative processes. However, recent findings of significant stenoses in the extracranial veins that drain the brain and spinal cord shed new light on these MR results. With the assumption that a majority, if not all, of multiple sclerosis patients exhibit such extracranial venous obstacles, the perfusion MR images of multiple sclerosis patients should be reinterpreted. Perhaps ongoing MR studies with respect to extracranial venous hemodynamics may decipher some of the unsolved puzzles related to this neurologic disease.