Creutzfeld-Jacob disease (CJD) is a degenerative, invariably fatal brain disorder. Multiple sclerosis (MS) is a chronic, potentially disabling, immune-mediated inflammatory demyelinating disease of the central nervous system. Here, we report a 50-year-old woman who, two years after the diagnosis of relapsing remitting MS, developed altered consciousness, dystonic posture of the left hand and myoclonic jerks. Repeated brain MRI showed hyperintensities on T2 sequences in basal ganglia bilaterally and diffusion restriction in these areas, and, since typical EEG and CSF features were present, the diagnosis of CJD was made. To the best of our knowledge, this is the first report of a glatiramer acetate-treated MS patient who developed sporadic CJD. This combination is interesting in the light of recent data suggesting that CJD and MS may share similar mechanisms of "molecular mimicry" and autoimmunity. This case also emphasizes the importance of critically assessing every new symptom even in a patient with an established diagnosis of MS.