Infectious mononucleosis has been usually considered a benign disease of adolescence and young adulthood. The present paper describes a fatal case of infectious mononucleosis in a 2-year-old boy, whose complications included Reye syndrome. After recovering from the Reye syndrome, he subsequently died from granulocytopenia and septicemia. Other complications included hepatitis, pneumonitis, gingivostomatitis, gastrointestinal bleeding, thrombocytopenia, and an ampicillin rash. The death and complications resulting from this usually benign entity have received little attention in the pediatric literature, and should be recalled by pediatricians confronted with a febrile child.