In this study, we compared the ostracod species diversity in selected inland-water habitats of Lapland and Poland, and assessed the relationships between ostracod occurrence and abiotic environmental variables. In total, 41 species were collected, of which only 15 species were found in Lapland, as compared with 35 in Poland. Almost all species collected from the Lapland sites were eurybiontic and no clear differences were found between ostracod assemblages inhabiting different habitat types. We hypothesize that this homogeneity might be a consequence of the raised water level during the springtime snow melt, temporarily connecting various waterbodies. The main factors limiting distribution of ostracod species in Lapland appeared to be low pH and low ionic content of water. In Poland,predominantly stenobiontic species were observed. In temporary waters and peat-bogs of this area useful indicator species were identified.