In Czechoslovakia the yearly incidence of sarcoidosis has been followed-up from the year 1971 on the whole territory, in each of 112 districts separately. All together it makes no difference what diagnostic procedure has corroborated the diagnosis or whether the patient at the time when sarcoidosis was ascertained did or did not have any disturbances. The number relative to 100000 inhavitants of each district varied greatly up to the end of 1975, from 0 to 32 per 100000 people. In 10 districts it was higher than 6:100000. As the very districts with the highest incidence in 7 out of 10 districts adjoined the districts with the zero incidence it seems to be logical to resume that the zero incidence in none of the 21 districts was a real one. The sex and age distribution, the number of persons with histologically verified diagnosis, the intrathoracic and extrathoracic localisation of sarcoidosis and the distribution of the stages of intrathoracic sarcoidosis have been followed-up in 1442, respectively in 1839 patients observed in the last five years period. The necessity of a new prospective cooporative controlled study of the incidence of sarcoidosis in some European countries seems to be evident.