Zamboni et al proposed a new hypothesis for the pathomechanisms of multiple sclerosis (MS): chronic cerebrospinal venous insufficiency (CCSVI). Using Doppler ultrasound and venograms, they found severe extracranial venous stenosis in MS patients. They suggested that a venous obstruction in the neck caused a reflux back into the brain, which led to edema and demyelination. We examined the blood flow and the cross-sectional area of the internal jugular veins using Doppler ultrasound (Vivid 7 PRO, GE Health Japan, Tokyo) in 17 MS (8 males and 9 females; 20-58 years of age, median 38 years) and 11 neuromyelitis optica (NMO) Japanese patients (1 male and 10 females; 23-60 years of age, median 44 years). Nine of the 11 NMO patients were seropositive for anti-aquaporin4 antibodies. We did not find any obstruction or stenosis of the internal jugular veins in any patient. Other disorders such as bilateral internal and external jugular venous ligation or radical neck dissection, which result in venous stasis, are not known causes of demyelination in the central nervous system. Our data also does not support the hypothesis of CCSVI theory, despite the fact that our study was limited to a small group of patients and the examination was performed only using Doppler ultrasound.