Perforatella incarnata (O. F. Müll.) and P. vicina (Rossm.) are sometimes difficult to distinguish. Variation analysis of the two species, based on over 300 specimens from Poland (the Carpathians, Sudetes, Lower Silesia), was aimed at testing the diagnostic use of shell, genital and body colour characters. Most characters varied within and between populations, and the variation ranges of some characters of the two species overlapped. Syntopic P. incarnata and P. vicina showed a divergent character displacement. The characters of high diagnostic value are: shell colour and surface sculpture, and mantle colour pattern. The mantle colour pattern can be useful when identifying live specimens, and the surface sculpture can be crucial when examining fossil material.