The entire population of cystic fibrosis (CF) patients in Denmark diagnosed in the period January 1, 1945, to June 30, 1985, comprised 514 persons of whom 62 were diagnosed at autopsy. Of the remaining 452 patients, 372 were probands and 80 were secondary cases. The effect of a centralized treatment on the prognosis was evaluated using a Cox's regression model. Furthermore an incidence analysis was performed using probands including autopsies. Centralized treatment had a significantly beneficial effect on the prognosis (p = 0.02), the death intensity (hazard rate) being decreased by a factor of 0.60. It was calculated that at present 1 out of 4,760 newborn Danes may be diagnosed as suffering from CF before the age of 15 years, and 3% of the Danish population are heterozygotes for CF.