Creutzfeldt-Jakob disease (CJD) has a significant degree of clinical heterogeneity that is especially found in the features at onset. Here we present a patient with the sporadic form of CJD mimicking Wernicke encephalopathy. We first treated him with a high dose of thiamine; however, the vitamin B1 levels proved to be normal, which ruled out Wernicke encephalopathy. Meanwhile, his clinical condition progressively worsened and he developed a rapidly progressive cognitive disorder, mutism and myoclonus of the muscles. At this point, the diagnosis of CJD was most likely. The patient died two months after the first symptoms. Autopsy showed prion-protein depositions in several regions. Genetic analysis was negative for familial CJD. Those findings confirmed the diagnosis of ‘sporadic Creutzfeldt-Jakob disease’. CJD presents in a wide range of sequences and clinical symptoms. Therefore, recognition in the early stage can be difficult.