A new species of fish leech from Poland, Piscicola burresoni n. sp. (Piscicolidae), is described. The leech was found in 2007 on stones and on pike (Esox lucius L.) and chub (Leuciscus cephalus L.) in the Łyna River, Poland. The leech is small, relatively flattened, with a prominent coarctation between the trachelosome and urosome. The pigmentation is unique to the new species and it has 14 annuli with gonopores separated by 4 annuli. The receptaculum seminis consists of an elliptical aperture located at a distance of 3 annuli behind the female gonopore. The copulatory area on the clitellum is characteristic in the shape of a parallel ellipse. The vector tissue is in the form of a transverse plate below the oviduct outlet. For a complete description of the external morphology, a geometric–mathematical model of the leech body form was used.