During 1978-1990, 346 patients with sarcoidosis were enrolled in our institute. Of 346 patients, 295 patients were eligible for evaluation on the clinical course and prognosis. According of their clinical presentations, they were classified into 3 groups; severe, moderate and mild sarcoidosis. Of the 295 patients, 27 (9.2%) were classified as severe sarcoidosis who developed serious illness including involvement of the heart (8), lung (6), muscles (5), eyes (3), central nervous system (CNS) (3) or liver (2). The mean interval between the onset of disease to severe disability was 58.3 months. The interval was particularly long in those patients who presented with either pulmonary (100.8 months) or liver sarcoidosis (108 months). Of the 27 patients with severe sarcoidosis, 8 (29.6%) gradually became worse towards the end of their clinical course despite only mild clinical signs and symptoms at the first presentation. Therefore, the initial clinical symptoms and findings, including ocular involvement. ECG abnormalities, negative reaction to PPD, high value of serum angiotensin converting enzyme (ACE) and a small number of lymphocytes in peripheral blood, were not useful in predicting prognosis. The relationship between the maximum serum ACE value during the clinical course and the duration of the active phase was statistically significant in the 123 patients who were monitored throughout their course, suggesting that the maximum serum ACE may be a marker for assessing prognosis. Corticosteroid was administered to 76 patients (22%) with serious systemic involvement. They included 26 (96.4%) of the 27 severe sarcoidosis and 50 (37.9%) of the 132 moderate sarcoidosis. Patients with mild sarcoidosis did not receive corticosteroids.(ABSTRACT TRUNCATED AT 250 WORDS)