In the present study, sarcocysts of a Sarcocystis species infecting the gecko Hemidactylus turcicus was investigated by light and transmission electron microscopy. Six out of 26 (23%) H. turcicus were found to be infected with cysts of Sarcocystis. Examined muscle samples of different sites showed high intensity of infection in the tail and hind limb skeletal muscles. Microscopically visible cysts reached a mean size of 80 x 720 mum. These cysts are characterized by a light microscopically thick cyst wall and inner prominent septa dividing their interior into a large number of compartments enclosing the different zoites. Ultrastructural characteristics of the primary cyst wall and its long, mostly not upright protrusions were investigated. Two widely differentiated zoites (metrocytes and cyst merozoites) were clearly identified; they all showed the characteristic architecture of the Apicomplexa and especially that of the genus Sarcocystis. The about 5-7 mum sized cyst merozoites seemed to be differentiated into those being either poorly or richly supplied with reserve materials (amylopectin, lipids). This finding may indicate the existence of different developmental stages. Events of endodyogeny represented the only mode of reproduction inside the cysts. While comparing the morphology of these cysts with other descriptions of cysts in reptiles, they were described as a new species (Sarcocystis turcicii).