After an examination of the most important physiopathological alterations of splenectomised patients and on the basis of careful research into the literature on study and classification of post-splenectomy hyperthermia, the Authors stress the importance of infections in the genesis of such hyperthermia, until a few years ago defined as "sine causa". On the basis of the consideration that this fever is due to an infection acting on an area (the a-splenic area) which is more vulnerable as it is deprived of a certain part of the reticulo-endothelial system, it was possible to postulate and verify that such hyperthermia could arise only in patients with altered extra-splenic reticulo-endothelial system and hence does not normally occur in patients splenectomised for trauma. On the basis of extensive personal experience, the authors conclude by stressing the therapeutic principles which seem to be most suitable for management of this insidious complication of splenectomy.