We describe the causes of reactive hemophagocytic process in a retrospective study including 99 patients. The main diagnosis were: lymphomas (18 cases), pyogenic bacteria infections (15 cases), herpes virus infections (12 cases), other infections (multiple, parasitic, fungal, mycobacterial, unidentified) (11 cases), acute hepatitis (five cases), systemic lupus erythematosus (three cases). We also found numerous other diseases involving the reticuloendothelial system. The cause remained undetermined in 16 cases. Lymphoma accounted for 64% of the cases in previously healthy patients who had been febrile for more than 10 days at the time of the diagnosis of reactive hemophagocytic process, and for 31% in HIV-positive patients. Lymphomas were rare (5%) in non HIV-positive, immunosuppressed patients. In this setting and in previously healthy patients who had been febrile for less than 10 days, infectious diseases were widely dominant (respectively 60% and 86% of the cases). Those were mainly due to pyogenic bacteria and to herpes virus. A rapidly fatal evolution occurred in some cases of lymphomas-related hemophagocytic process. These data support the choice of aggressive investigations in order to diagnose lymphoma in previously healthy patients presenting with reactive hemophagocytic process who have been febrile for more than 10 days, and in selected HIV-patients. Such a procedure is not recommended in the other cases.