Chromosome characteristics of Trichobilharzia franki Müller et Kimming, 1994, causing swimmer's itch in the Western Germany, were described and compared with the karyotype of the sympatric species Trichobilharzia szidali Neuhaus, 1952. Karyotypes of both species are very similar: diploid sets consist of seven pairs of autosome chromosomes and one pair of sex chromosomes (2n = 16, n = 5m + 2sm + Zsm/Wst), the sex determining mechanism is ZZ in males and ZW in females and gross morphology of autosome pairs does not differ markedly. The only clear discriminative feature lies in the size and shape of sex chromosomes.