The key problem of epidemiological methodology is the choice of representative sample for a population. Epidemiological analysis is based on geographical information system data, which use data obtained from HIS. Such systems store personal identifi cation numbers (PESEL) matched with territorial codes (TERYT) and postal address numbers (PNA). At the same time, a question about the credibility of recorded information arises.

Goal. To examine the credibility of personal and address data stored in HIS, for later use of those data to epidemiologic analysis.

Materials and methods. PESEL and TERYT codes obtained from HIS and TERYT codes (matched with the time of hospitalisation) were obtained from PESEL population registration database. The equality of data obtained from HIS and PESEL population registration systems was compared using a database built with Divmod Axiom database engine.

Results. It was impossible to determine the PESEL number only for 2.61% of HIS records. Similarly, only for 1.82% of HIS records it was not possible to locate TERYT code in PESEL database. Recorded information regarding deaths was equal for both PESEL and HIS. Differences in address data was noticed in 937 hospitalisation records (40.93% of examined hospitalisations). 622 cases (27.17% examined hospitalisations) regarded the differentiation between urban and rural municipality in case both had the same name, but different TERYT code.

Conclusion. The use of PESEL personal identifi cation number to identify the patient and the quality of death records are credible enough to be included in epidemiological analysis. Using of TERYT code recorded in HIS to identify patient’s address data is likely to be erroneous; this justifies usage of PESEL population registration database to obtain the TERYT code. The use of PNA code and mapping PNA code to TERYT also seems to be justified; doing so should raise the quality and the credibility of geographical epidemiological analysis.