Multiple sclerosis (MS) is characterized by inflammation, demyelination and gliosis, involving the central nervous system (CNS) and commonly sparing the peripheral nervous system (PNS). Coexistence of CNS and PNS chronic demyelination has been rarely demonstrated in chronic inflammatory demyelinating polyradiculoneuropathies (CIDP) and in MS, but the occurrence of acute polyradiculoneuropathy in a patient with MS is even more unusual. We describe the case of a woman with relapsing-remitting MS who presented with an acute severe tetraparesis. Cerebrospinal fluid (CSF) examination together with neurophysiological data and sural nerve biopsy study demonstrated an axonal form of Guillain-Barré Syndrome (GBS). It remains unresolved if the association of an axonal form of GBS and MS is fortuitous or, on the contrary, is indicative of the coexistence in some individuals of common pathogenetic mechanisms.