We describe the first case of hyperacute reversible encephalopathy following COVID-19 vaccination. A patient presented with acute onset encephalopathy, mainly characterized by agitation and confusion, rapidly responsive to high dosage steroid therapy and complete remission within 3 days from onset. The clinical manifestation was related with systemic and CSF cytokine hyperproduction, responsive to steroid therapy. Although the occurrence of encephalopathy after vaccination may be just a casual temporal association, we speculate that the cytokine-storm could be the result of an excessive innate immune response against the vaccine, in a predisposed patient susceptible to autoimmunity.