Infectious mononucleosis (IM) is usually considered a benign disease. Agranulocytosis developed in a young college student 14 days after the onset of IM. Fulminant staphylococcal pneumonia and bilateral pulmonary infarcts resulted, and the patient died 4 1/2 hours after admission to a hospital. Agranulocytosis secondary to IM may be more prevalent than previously thought. A review of the literature indicated that infection developed in 57.9% of the patients with IM and extreme neutropenia and 45.4% of the infected patients died.