deltaF508 is the most common (70%) among over 1000 mutations of the gene encoding ATP-regulated chloride channel, namely CFTR--cystic fibrosis transmembrane regulator. The time which passed from the calculated mutation event was anticipated on the basis of the frequency of contemporary haplotypes, but not on its direct identification. The presence of three base pairs deletion in the ancient DNA (aDNA) isolated from skeletal remains of the Middle Ages origin was investigated. Teeth excavated in the area of three sites located in Central Poland were processed for a DNA. 6 out of 82 samples did not produce amplificable fragments of DNA. Although the number of specimens analyzed was sufficient to confirm the presence of the rare mutation, the deltaF508 CFTR sequence was not found in the remains of individuals living back 35 - 45 generations. The absence of the mutated allele in the particular geographic region cannot state for the status of mutated allele throughout the country, especially at times when migrations were limited and movements of people were more area restricted than at present days.