Neutropenia, a below normal concentration of neutrophils in the circulating blood, can be the kinetic result of diminished neutrophil production, excessive neutrophil margination, or accelerated neutrophil utilization and destruction. The significance of neutropenia to the well-being of the subject is dependent, in part, on the responsible kinetic mechanism. In this review of the causes of neutropenia in newborn infants, the authors examine neutrophil production and kinetics in the human fetus and newborn infant. The recognized causes of neutropenia in neonates are categorized and discussed according to their underlying kinetic mechanism.