Wernicke encephalopathy (WE) commonly presents with oculomotor abnormalities, gait ataxia and confusion. WE can mimic rapidly progressive dementia syndromes, such as Creutzfeldt-Jakob disease (CJD). Cerebrospinal fluid (CSF) tau is frequently used for diagnosis of several dementia subtypes, predominantly CJD and Alzheimer's disease. The combination of very high CSF tau (tau) and normal phosphorylated tau (p-tau) levels is almost exclusively seen in aggressive diseases, such as CJD. The authors present a case of a woman with WE, caused by chronic insufficient dietary intake, with highly elevated CSF tau and normal p-tau. The clinical symptoms and CSF findings raised the suspicion of CJD. However, shortly after immediate treatment with thiamine the patient clinically improved. At follow-up, 2.5 months later, she had made a good recovery. This case of rapidly progressive dementia illustrates that, even in the case of a highly elevated CSF tau, clinicians should be alert for treatable causes such as WE.