BACKGROUND Molecular genetics are a fundamental turning point in the approach to autosomal dominant hereditary renal polycystosis of adults (ADPKD). DNA analysis makes diagnosis possible at in any ontogenic period, i.e. also during the prenatal period. The objective of the present study was to test the presymptomatic DNA diagnosis in a major group of patients with ADPKD and the possibility to detect the disease in the initial stage and influence its development by early treatment and advise the patients on parenthood. RESULTS In 1990-1994 the authors contacted 157 patients with polycystic kidney disease, adult type (ADPKD). 87 families were examined by Southern's RFLP method (gene PKD1, 16p13.3, standard probe 3'HVR and restrictase Pvu II). Of 493 members of these families only 25 (5.1%) refused to be examined. So far 378 examinations were completed, 90 proceed. In 40 of 132 examined subjects with the risk of ADPKD transmission of the gene was proved. Of four examinations of the foetus with the risk of ADPKD twice transmission of the gene was proved and the pregnancy was terminated. In three families with three or more members suffering from ADPKD in some there was not agreement between the result of linkage analysis of DNA and the clinical finding. The authors analyzed whether the cause is recombination or ADKPD conditioned by mutation of gene PKD2 (4p13-23). Linkage analysis remains in ADPKD the basic examination as the sequence of gene PKD1 is not yet completed. Discovery of gene PKD2 the mutations of which condition as many as 15% of all cases of ADPKD has an impact on the evaluation of linkage analysis. The reliability of prediction rises with the number of examined subjects in the family. The examination revealed that patients are willing to have DNA examinations (as many as 98%); despite this the number of examined subjects is only a small fraction of the anticipated 10,000 people in the Czech Republic suffering from ADPKD: CONCLUSIONS DNA analysis in patients with autosomal dominant polycystic kidney disease is the most important examination for its diagnosis. It makes the diagnosis possible in all stages of ontogenesis, incl. prenatal diagnosis. It is a highly valid parameter when these patients decide on parenthood. It makes early treatment possible which can influence the development of the disease and its complications.