Adult onset Still's disease (AOSD) is a rare systemic inflammatory disorder affecting mainly young adults. AOSD is characterized clinically by spiking fever, arthritis, evanescent rash, sore throat, enlargement of lymph nodes and splenomegaly, and biologically by neutrophilic leukocytosis, high levels of ferritine and elevated liver enzymes. None of these features are specific, and although several classification criteria have been proposed, AOSD remains a diagnosis by exclusion. Its causes and pathomechanism are still unknown, although there is increasing evidence of dysregulated innate immune response. Treatment mainstays are systemic corticosteroids and methotrexate. Blockade of proinflammatory cytokines may be effective in the substantial proportion of patients with poor response to classical immunosuppressants.