Cystic fibrosis is the most common, severe, inherited disease in the Caucasian 
population. As a consequence, the demand for genetic counselling of patients 
with cystic fibrosis and their families is large. In Denmark the incidence of 
cystic fibrosis is 1:4700, which is quite low compared to other European 
countries. We have investigated 268 Danish cystic fibrosis patients with respect 
to DNA markers (haplotypes) and the most common mutation delta F508. The delta 
F508 mutation is found on 88% of all cystic fibrosis chromosomes, the highest 
frequency reported so far. This had had an important impact on genetic 
counselling, prenatal diagnosis and eventually population screening. In the 
Danish population 78% of all couples at risk will be informative for delta F508 
and will be identifiable by simple screening methods.