Morphology and anatomy of 20 Central European populations of the spring snail Bythinella Moquin-Tandon are described and illustrated. Detailed descriptions, drawings and SEM photographs, as well as measurements of shells, opercula, radulae and soft parts are presented, special attention being paid to the reproductive organs. Intrapopulation and interpopulation differences in 40 biometrical characters in males and 42 in females are analysed, for each sex separately, by means of descriptive statistics and ANOVA. Relations between variables are tested with Kendall’s correlation coefficient. Biometrical characters vary widely within and slightly between the studied populations, whose variability ranges overlap. The length ratios: shell/radula, bursa/bursa duct and bursa/receptacle, as well as the length of bursa copulatrix and ctenidium display a statistically significant S–N clinal variation. The wide intrapopulation variation combined with the slight differences between the distinguished morphospecies in almost all the morphological characters examined indicates a limited diagnostic value of these characters in Bythinella.