A 15-year study of patients with sarcoidosis is presented. In most patients, the disease was discovered at a general health screening examination. The mean total incidence among persons 15 yr of age or older was 19 per 100,000 per year (21.7 for women and 16.5 for men). There was a peak incidence in both sexes between the ages of 20 and 34, and in older women, there was a second but lower and broader peak. The frequency of symptoms was greater in older women than in other patients. The accumulated lifetime risk of sarcoidosis was 1.3% for women and almost 1% for men. Patients with Stage I sarcoidosis, i.e., with bilateral hilar adenopathy alone, had the best prognosis, with 50% of the patients showing a normal radiographic picture 15 months after the discovery of the disease. Among patients with Stage II sarcoidosis (both bilateral hilar adenopathy and pulmonary infiltration), it was 36 months before 50% returned to normal radiographically. Resolution of all radiographic evidence of the disease could still occur many years after the first pathologic findings were made on chest films.