Here we report a novel haemodynamic signal using BOLD-weighted fMRI that is restricted to the internal cerebral veins and identifiable in all subjects assessed to date. This signal is oscillatory with peak power at 0.054 Hz. In early MS patients, venous power was diminished compared to controls. Venous power was inversely correlated with T2 lesion volume but not brain atrophy. These results indicate that neuroinflammation is associated with altered venous haemodynamics that could be attributable to venous structural damage previously reported in MS. This novel venous signal should also be investigated more broadly in cerebrovascular disease.