Alloimmune neonatal neutropenia (ANN) is an uncommon but potentially life-threatening disorder of the neonate and young infant. Hematologically, the mother's peripheral neutrophil count is normal. However, the passive transfer of maternal immunoglobulin G neutrophil-specific antibodies and the subsequent sensitization of fetal neutrophils can result in severe neutropenia in the neonate. Generally, ANN is a self-limiting condition, but with severe bacterial infection, mortality can be high. We present the clinical features of monozygous twins delivered at 33 weeks' postconception with this condition. This case report is unique in that it occurred in twins born prematurely and was attributable to antibodies against 2 neutrophil-specific antigens, NA1 and NB1. A brief review of the diagnosis, management, and treatment of ANN is presented.