A lymph node biopsy sample from a boy aged with fever, pneumonia, hepatosplenomegaly, lymphadenopathy and pancytopenia, showed histiocytosis with erythrophagocytosis, compatible with the haemophagocytic syndrome. Treatment consisted of dexamethasone and etoposide, with cyclosporine added in a later phase. During the subsequent remission phase, bone marrow transplantation was carried out. Haemophagocytic syndrome is a rare condition, characterized by fever, pancytopenia, hepatosplenomegaly and characteristic laboratory findings (including a high interferon-gamma level) and morbid-anatomical findings (haemophagocytic histiocytic cells in bone marrow, lymph nodes, liver and spleen, but also in the CNS, kidneys and lungs). Recent pathophysiological discoveries indicate an enhanced T-cell response, leading to hypercytokinaemia. As a rule the patient dies from multiorgan failure and diffuse intravascular coagulation. Bone marrow transplantation is the treatment of choice.