We analyzed the prognostic value of Tau protein, a marker of axonal damage, detected in the cerebrospinal fluid (CSF) of patients with relapsing-remitting multiple sclerosis (RRMS). We sampled the CSF from 32 patients with probable or definite RRMS, having had the disease for less than 5 years. We studied the relationship between Tau protein concentration in the CSF (CSF-TAU) and disability, time to next relapse and time to experience a one point increase on the Expanded Disability Status Scale (EDSS). CSF-TAU was correlated with the Progression Index at the end of follow-up. Patients with higher CSF-TAU experienced a more rapid one point increase in the EDSS. CSF-TAU was the only independent variable to predict the time to next relapse. CSF-TAU, as a marker of axonal loss, may help us to predict short-term outcome in patients with early RRMS.