We report two siblings with autoimmune neutropenia of infancy. Patient 1 was hospitalized for viral gastroenteritis at 5 months of age, when his absolute neutrophil count was 684/mm3. Absolute neutrophil counts ranging from 0 to 930/mm3 continued but normalized spontaneously at 25 months of age. Patient 2, a younger brother of patient 1, had prolonged high grade fever at 5 months, when his absolute neutrophil count was 138/mm3. Absolute neutrophil counts ranging from 96 to 1,078/mm3 continued for the following 9 months. Antineutrophil antibodies were detected in the patients' sera. Our cases are siblings and each case was independently affected, since the diagnoses were made at 5 months of age and the interval between the diagnoses was 23 months. Autoimmune neutropenia of infancy is comparatively rare, so that we think that the disease in these siblings was due to a genetic abnormality.