In 2009 a novel swine-origin Influenza A H1N1 virus was identified in Mexico and Southern California. Since it was first recognized, neurological complications including acute necrotizing encephalopathy (ANE) have been globally documented in association with this viral infection. ANE is mostly known to occur in the paediatric population. We describe a fatal case of ANE in a previously healthy 40-year-old man infected with influenza A H1N1 virus presenting with severe neurologic decline. Computed tomography (CT) scan and magnetic resonance imaging (MRI) findings were consistent with ANE. CT and MR findings typically documented in paediatric cases of ANE - including bilateral thalamic necrosis with petechial hemorrhage - have been seldom described in adulthood.