Seven thrush species (Turdidae) from Costa Rica were examined for intestinal parasites; 21 of the 84 (25%) birds sampled were positive for a new species of Isospora. Oocysts of Isospora zorzali n. sp. have thin, smooth, double, and colorless walls; they measure 19.7 ± 1.5 µm × 18.6 ± 1.4 µm (16–24 µm × 15–21 µm), with an average length–width ratio of 1.1 µm. Sporocysts are ovoid, measure 8.5 ± 1.1 µm × 14.5 ± 1.7 µm (7–11 µm × 11–18 µm) with an average length–width ratio of 1.7 µm. A nipple-like stieda body continuous with the sporocyst wall is present, but no substieda body was observed. A sporocyst residuum consisting of large equal sized granules was observed either clumped together or diffusely. The sporocysts fill the entire oocysts with little to no open space observed. This is the first report of Isospora species from any of the sampled host species and also the first report from any species of thrush in Costa Rica.