Adult-onset Still's disease (AOSD) is a rare systemic inflammatory disorder characterised by high spiking fever, an evanescent salmon pink rash and arthritis, frequently accompanied by sore throat, myalgias, lymphadenopathies, splenomegaly and neutrophilic leukocytosis. Aetiology is still unknown, however, it seems that an important role is played by various infectious agents, which would act as triggers in genetically predisposed hosts. Diagnosis is a clinical one and may be lengthy because it requires exclusion of infectious neoplasms, including malignant lymphomas and leukaemias, and other autoimmune diseases. Different diagnostic or classification criteria have been proposed, but not definitely accepted. There are no specific laboratory tests for AOSD, but they reflect the systemic inflammation: the ESR is consistently high, while the rheumatoid factors and antinuclear antibodies are negative. High serum ferritin levels associated with a low fraction of its glycosylated component are assessed as useful diagnostic and disease activity markers. The clinical course can be divided into three main patterns with different prognoses: self-limited or monophasic, intermittent or polycyclic systemic and chronic articular pattern. Therapy includes non-steroidal anti-inflammatory drugs, corticosteroids and disease modifying anti-rheumatic drugs: biological agents have recently been introduced and they seem to be very promising not only for the treatment but also for understanding the pathogenic mechanisms underlying the disease.