It is demonstrated that the diversity of Bythinella species in Bulgaria is higher than was formerly realised. The Balkan Peninsula is probably a major centre of endemicity for the genus Bythinella, and more species are expected, as some of the localities pointed out in the old literature were not investigated (Vitosha Mts, Petrokhan Pass in Stara planina Mts). We found eleven new Bythinella spp., 7 species in springs and 4 species in small streams. The vertical spread of Bythinella spp. in Bulgaria is not wide, with 14 species living below 1000 m a.s.l., 13 of them below 500 m, and only 3 species reaching springs higher than 1000 m. Multivariate cluster analysis reveals the distinctness of the newly described species and an identification key to the 17 Bythinella spp. known so far from Bulgaria is provided.