DNA sequences of the mitochondrial cox1 gene were analysed in 4 new local populations of Sinanodonta woodiana (Bivalvia) in Poland, in the first reported Polish population, and in a population from Hungary. The gene sequences of Polish specimens were identical to those of specimens from Hungary, Italy and Ukraine, but different from those of Romanian specimens (data from GenBank). According to fish farm documentation, S. woodiana had spread in Poland by 2 routes: i) direct import of fish infected by glochidia of S. woodiana from Hungary; and ii) indirectly, by the major distributor of thermophilous fish in Poland, Gosławice Fish Farm, which started to import Hungarian fish in the 1960s. The genetic analysis and available documentation unambiguously confirm that Polish populations of S. woodiana derive from a source population in Hungary. In addition, we noticed doubtful identification of this species in GenBank data and further research is needed to resolve this problem.