Adult-onset Still's disease (AOSD) is a systemic inflammatory disorder of unknown etiology and pathogenesis. AOSD is a rare condition, usually presenting with high fever accompanied by systemic manifestations. The disease is a heterogeneous pathological entity with a range of etiologies, manifestations and prognosis. There is no single diagnostic test for AOSD; rather, the diagnosis is based upon clinical criteria such as arthralgia, fever, skin rash, lymphadenopathy, and hepatosplenomegaly. Determination of the procalcitonin level and the biological response to empirical corticosteroid therapy generally helps the diagnosis, while immune-serology, as a 'screening' test, will not add meaningful information in most cases. Treatment consists of anti-inflammatory medications. Non-steroid anti-inflammatory drugs have limited efficacy, corticosteroid therapy and disease-modifying antirheumatic drugs are usually required. Novel therapeutic approaches, such as anti-tumor necrosis factor blockade and stem cell transplantation, are promising. In this chapter we present clinical and laboratory parameters of 18 patients diagnosed with AOSD at our institution between 1997 and 2003, and review the literature.