The phenomenon of geographic variation is known in practically all taxa of living beings. However, the reality of this phenomenon in freshwater molluscs (snails and bivalves) has many times been questioned in the past. It was accepted that these animals do not demonstrate spatially-oriented variation, and specific "local race" is arisen in each concrete habitat. Terentiev (1970a) was the first student to show statistically that there are real geographic clines in freshwater molluscs. Since the Terentiev's work, a few species of freshwater molluscs has been studied in this respect, therefore it is almost impossible to draw any general patterns of geographical variation in this group of animals. However, most species of freshwater molluscs studied to the date exhibit statistically significant decrease of their body size in the south-north direction. Perhaps, it may be explained by decrease of the length of the growth season in high latitudes. Some species of freshwater snails demonstrate clinal changes in shell proportions. It allows us to reject subspecies separation within these species since diagnostic characters of such "subspecies" may blur when geographic variation is taken into consideration. The data on geographic variation in anatomical traits in freshwater molluscs are much more scarce. At least one species of pond snails (Lymnaea terebra) demonstrates clinal variation in proportions of its copulative apparatus in the south-north direction. Further studies of geographic variation in freshwater molluscs should reveal if it is truly adaptive, i.e. whether geographical clines have underlying genetic basis. Otherwise, the clines may arise as a result of direct modificating effect of an environment.