: The EEG is helpful in the evaluation of patients with altered mental status and can provide clues for the underlying cause of certain entities. There are few descriptions of the EEG findings in patients with West Nile virus (WNV) infection. We describe the clinical presentation as well as the electroencephalographic findings in five patients with WNV encephalitis. Review of the records of all cases of WNV infection seen at the Mayo Clinic from 1999 to 2003, in which an EEG had been performed. Five patients with WNV encephalitis, in whom an EEG was performed, were found. All the patients had altered mental status and the EEG showed moderate to severe degrees of generalized slowing. Three of the patients had triphasic waves on the EEG. The patients did not have any metabolic disorder or electrolyte abnormalities that could account for these findings. EEG findings in WNV are consistent with an encephalopathic pattern and show varying degrees of generalized slow wave abnormalities and in some cases triphasic waves.