Genetic variation in the pulmonate land snail Zonitoides nitidus was examined by means of allozyme electrophoresis in 17 European populations. We observed no heterozygotes, indicating that Z. nitidus consists of several homozygous multilocus genotypes (strains) probably produced by self-fertilization. Nine strains were detected. Strains appeared not to be equally distributed over the regions considered. One strain was strongly differentiated from the others, which is suggestive of a taxonomic differentiation. Anatomically, two major phally types were distinguished: euphallics, with well-developed male reproductive organs, and hemiphallics, with weakly developed male reproductive organs. Both phally types were found together in natural populations, but euphally ratios were very low (0–19%; overall mean = 7.79%) and differed between geographical regions (Belgium, Germany, and Sweden). In some populations, hemiphallic individuals were smaller compared to euphallic individuals although the difference is small and its biological significance remains to be established. We found no clear relation between phally type and allozyme data.