This syndrome is characterized by a hyper-triglyceridemia associated with a deficiency of the plasma lipolytic activity induced by heparin infusion. All signes ascribed to familial lymphohistocytosis were found in this patient. When a diagnosis of acute reticulosis in children is made, such biological characteristics should be searched for. Since in systemic lupus erythematosus an acquired and analogous type of hyperlipidemia has been described, the hypothesis of an immunological pathogenesis in familial lymphohistiocytosis may be plausible.