OBJECTIVE: To understand the clinical manifestations and disease course of adult onset Still' s disease (AOSD). METHODS: 15 patients of AOSD diagnosed at Severance hospital, Yonsei University College of Medicine were retrospectively analysed in the period of September 1988 to September 1995. RESULTS: There were 3 men and 12 women (male to female ratio of 1:4). Age of disease onset ranged from 17-55 years, and over 86% of the patients were younger than age 40 at disease onset. The prevalence of clinical features were as follows fever (100%), arthritis (93%), skin rash (93%), sore throat (60%), abnormal liver function (73%), lymphadenopathy (47%), splenomegaly (47%), hepatomegaly (20%), serositis (13%). Fever was the most common initial symptom. Common labaratory features were leukocytosis with neutrophilia (87%), anemia' Hgb <10 g/dL (67%), increased serum ferritin (83%), ESR (87%) and CRP (93%). Serum ferritin was markedly raised at disease onset and correlated with disease activity. In 2 patients, the disease was controlled with NSAID alone, but most of the patients required steroid to control the disease activity. In 6 patients, MTX was added for steroid sparing effect and for steroid resistant arthritis. Most of AOSD patients had intermittent and chronic disease course. Root joint arthritis and polyarthritis were factors associated with chronicity. CONCLUSION: The clinical features of AOSD in our study generally resemble previous reports. Serum ferritin was a useful marker of disease activity. Most patients of AOSD had intermittent and chronic disease course. Root joint athritis and polyarticular pattern at disease onset were factors associated with chronicity.