Atraumatic Clostridium septicum infection is rare in infancy and childhood and is associated with a high mortality rate. Although in adults it has been reported to occur mainly in patients with gastrointestinal malignancy, pediatric cases were always associated with neutropenia. About 70% of the cases were described in children with neutropenia caused by chemotherapy and 30% were found in children with cyclic neutropenia. No case was described in children with other forms of congenital severe neutropenia. We describe three children with cyclic neutropenia and severe Clostridium septicum infection, discuss the various possibilities of causation, and the need for prompt and aggressive treatment of this serious condition.