The incidence and clinical picture of sarcoidosis were studied on the basis of an unselected series of 354 sarcoidosis patients (168 men, 186 women) in a defined geographical area during the years 1970–1981. All the patients were examined in hospital. The mean annual incidence of sarcoidosis was 15 cases per 100 000 population 15 years or older. Sixty-four per cent of the cases began or were diagnosed in the first half of the year (P<0.001). The disease was diagnosed in 67% of the male cases and 38% of the females before the age of 35. Sarcoidosis was found by mass chest radiographic survey or by chance in 99 men (59%) and 103 women (55%), but 85 men (51%) and 129 women (69%) had symptoms of the disease. Two hundred and eighteen patients (62%) had bilateral hilar adenopathy upon diagnosis of the disease, 120 (34%) parenchymal changes and three fibrotic radiographic changes. Lung function test results tended to decrease with the radiographic stage and were indicative more of obstruction than restriction.