Background: Powassan virus is a tick borne virus which can lead to encephalitis. Methods: 63 year old woman with history of migraine presented with 2 days of fever, headache, language difficulty and right sided facial droop. Her examination revealed right upper motor neuron type facial weakness and expressive aphasia. She rapidly deteriorated within 24 hours becoming non verbal and ultimately comatose. Results: MRI brain revealed T2 hyperintensities in bilateral caudate and putamen. Subsequent MRI brain showed progression of the caudate and basal ganglia changes and new T2 hyperintensities in bilateral thalami and midbrain with no abnormal enhancement. CSF revealed lymphocytic pleocytosis with normal protein and glucose. Viral Encephalitis was suspected and she was continued on Acyclovir until Varicella zoster and Herpes simplex virus serology in CSF returned negative. Prolonged video EEG showed near continuous generalized triphasic pattern without any evolution or seizure pattern. There was no improvement in clinical status or EEG with antiepileptic treatment. Paraneoplastic panel , serum HIV, Lyme and 14-3-3 protein were negative. Extensive viral serologies were sent and ultimately Powassan serology came back positive. Conclusions: This case highlights powassan virus as a cause of encephalitis and occurrence of triphasic waves in non metabolic causes of encephalopathy such as infectious encephalitis.