Sixteen patients with adult onset Still's disease are reported and compared to 42 previously reported cases. The onset of this illness is sudden and is characterized by quotidian fever, evanescent rash, arthritis, leukocytosis and with variable frequency abnormalities of the liver function tests, adenopathy, splenomegaly and loss of weight. The response to anti-inflammatory therapy is satisfactory and the majority of patients will have a good functional prognosis even though they may require corticosteroids to suppress the signs and symptoms of the disease. It is stressed that Still's disease should be considered one of the diagnostic possibilities in cases of fever of unknown etiology and in cases of seronegative arthritis in adult patients. The pertinent clinical, laboratory, radiological and histological features of this illness are reviewed.