[A rare differential diagnosis of fever of unknown origin].

A 22-year-old male patient with a clinical picture similar to that of sepsis was diagnosed with macrophage activation syndrome in adult Still's disease on the basis of clinical and laboratory criteria. The diagnostic work-up included the differentiated clarification of a persistent fever syndrome and the differential diagnosis of hemophagocytic lymphohistiocytosis. Immunosuppressive therapy with dexamethasone, immunoglobulins and anakinra was initiated and a sustained clinical remission was achieved.