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A new coccidian species (Protozoa: Apicomplexa: Isospora) is described parasitizing white-necked thrushes Turdus albicollis Vieillot, 1818; rufous-bellied thrushes Turdus rufiventris Vieillot, 1818; pale-breasted thrushes Turdus leucomelas Vieillot, 1818; and yellow-legged thrushes Turdus flavipes Vieillot, 1818 from 3 different localities in Brazil. Isospora sabiai n. sp. has oocysts that are subspherical to ellipsoidal, 20.9 × 18.6 μm, with smooth, delicate, bilayered wall, ∼1.1 μm thick. Micropyle inconspicuous or imperceptible. Oocyst residuum absent, but small polar granules rounded or comma-shaped are present. Sporocysts are elongate ellipsoidal to reniform, 16.5 × 9.2 μm. The Stieda body is knob-like. Sub-Stieda body rounded to conical, sometimes homogeneous with the Stieda body. Sporocyst residuum is present, usually as a cluster of numerous granules. Sporozoites are vermiform with 2 refractile bodies. The oocysts and sporocysts of I. sabiai n. sp. are uniform in the proportionality of width on length, but exhibited different patterns of size associated with each host species; therefore, an ecological discussion is introduced aimed at associating these morphometrical patterns of the oocysts with the habits of the different species of thrushes. This is the seventh isosporoid coccidian reported from New World turdids.