The paper describes morphometric and allozymic differences between 20 Central European populations of Bythinella. Morphometric differences were studied using principal component analysis, based on 40 biometrical characters in males and 42 in females, for each sex separately. The results showed a slight interand a wide intrapopulation morphometric variation, the variability ranges of the populations and postulated morphospecies overlapping. To visualize the pattern of interpopulation allozymic differences, studied at 9 loci, correspondence analysis of allele frequencies and multidimensional scaling based on genetic distances (Prevosti, unbiased Nei and Cavalli-Sforza and Edwards arc distance) were used. The values of Nei distances between populations (0.000–0.362) ranged from ones typical of conspecific populations (in the majority of populations) to ones characteristic rather of congeneric species. The patterns of interpopulation distinctness for molecular and morphological data were different and did not unequivocally confirm either the morphological or molecular distinctness of the distinguished morphospecies. All the genetic distances and Euclidean (morphology-based) distances were correlated with geographic distances, whereas no significant correlations were observed between the genetic and Euclidean distances.