One type of sarcocyst was found in two of eight investigated jackdaws (Corvus monedula) and proposed as Sarcocystis corvusi sp. nov. By light microscope, cysts resembled a thick thread and were very long (the largest fragment found amounted to 6 mm) and relatively thin (up to 60 μm). The cyst wall measured <1 μm and seemed smooth. Using a computerized image analysis system, knolls, which resembled protrusions, were visible on the wall surface. Ultrastructurally, the cyst wall was wavy and reached up to 1.1 μm. The waves were of different heights and resembled low protrusions. The parasitophorous vacuolar membrane had many invaginations. Lancet- or orange segment-shaped cystozoites were 5.9-7.3 μm long. These sarcocysts had type-1 tissue cyst wall. According to 18S rRNA, 28S rRNA genes and ITS-1 region sequences, it was shown that S. corvusi is a genetically separate species. On the basis of these genetic markers, S. corvusi was most closely related to S. columbae, S. calchasi and S. wobeseri which parasitize birds and are characterized by the same type of sarcocyst wall.