Bioindication assessment of water bodies of Ukraine can be carried out using the ratio of males and females of mollusks of the genus Viviparus. In practice, it is very convenient to determine the sex of mollusks by the differences in their shell. Male and female freshwater snails Viviparus viviparus (Linnaeus, 1758) and V. contectus (Millet, 1813) are shown to have reliable differences in shell morphology depending on their age. There is almost no sexual dimorphism by shell morphometrics and indices in Viviparus snails aged one to three years. After three years of life, mature females have significantly larger shell width, higher body whorl, and size of the aperture. Females of V. viviparus at the age of two to five years may be differentiated from males by the relationship of mean shell width and shell height, which is statistically significant higher than in males. This difference is explained by the different size of the mantle section genital organs of mature male and female. The obtained results should be taken into consideration in establishing the sex of viviparid snails