In the district of middle-Slovakia with 1.400.000 inhabitants preventive mass-X-ray examinations of the population over 15 years were made to find tuberculosis patients. Suspicious cases got a solid investigation in the hospital departments for tuberculosis and respiratory diseases or in special lung clinics. Every year nearly 500000 radiophotographs are produced for mass-X-ray, before start in profession, for people with higher risk of disease, for boys liable to military service and persons with tuberculosis contacts. As we could confirm in the investigation of suspicious cases the diagnosis "Sarcoidosis" in some departments we follow up its incidence and prevalence since 1971. In our district we detect about 50 new cases every year. That corresponds to an incidence of 3.5 per 100000 inhabitants. There are great differences between the single departments from 0.65 to 15.2 per 100000 inhabitants. This counts for a regional distribution. Since five years we similar follow the prevalence, which had an average of 14.9 per 100000 in 1971 in our district and of 27.7 per 100.000 in 1975. The prevalence of sarcoidosis differs between 12 and 51 per 100000 inhabitants in the single department of our districts.