We report the case of a boy 5 years old we admitted to our PICU with signs of impending hepatic failure (hypertransaminasemia, hyperammonemia, prolonged PT) following mild upper respiratory infection and irrepressible vomiting. We observed no neurological abnormalities excepting slight lethargy; on the contrary, EEG findings showed severe diffuse slowing and high-voltage Delta activity. Our diagnosis of Reye's syndrome was later confirmed by liver biopsy. Clinical and electrophysiological signs recovered after 48-72 hours and no explication was found for this anomalous Reye's syndrome presentation. Further studies are needed for understanding the basis of neurological involvement of stage I Reye's syndrome.