The adult Still's disease (ASD) is an uncommon inflammatory systemic disorder which affects the young adult. It is characterized by high spiking fever, vanishing rash, oligopolyarthritis, neutrophilic leucocytosis, negative titers for rheumatoid factor and antinuclear antibodies. Polyserositis, sore throat, uveitis are sometimes present and in one third of the cases it is possible to find hepato-splenomegaly with lymph node enlargement. G. Still first described the disease in child, in 1897, and in the adult it was recognized as a nosologic entity more than 70 years later. The ASD diagnosis is difficult and it is possible after the exclusion of many other diseases. Clinical manifestation are all nonspecific. In particular the presence of adenopathy, hepato-splenomegaly may suggest the possibility of a malignant lymphoma. Important exclusions include many other diseases such as the rheumatic fever, periodic fever, Lyme disease. At the same time a probable diagnosis of ASD should be considered in all the cases of high fever with rash, arthritis, neutrophilic leucocytosis or in the cases of fever of unknown origin (FUO). The prognosis is considered overall benign. The disease is usually sensible to salicylate treatment, even but the association with corticosteroids or, sometimes, with cytotoxic therapy is often required.