The case of a 24-year-old man with neutropenia of possible chronic, congenital origin is discussed. During hospitalization there were two separate bacterial infections plus a hemolytic crisis secondary to infectious mononucleosis. There was a neutrophilic production defect with a hypoplastic marrow showing a maturation arrest at the myelocytic stage except during a single episode of relative neutrophilia, when mature neutrophils were seen. The patient had a past history of severe periodontal disease with subsequent virtual full-mouth dental extractions. The presenting symptom at this time was an oral ulcer, and it is suggested that this may be one of the first signs of neutropenia. © 1969.