This article reports on a golden-billed saltator Saltator aurantiirostris Vieillot, 1817, kept in captivity outside its natural distribution area, in the proximities of the Itatiaia National Park, as a new host for Isospora similisi Coelho, Berto, Neves, Oliveira, Flausino & Lopes, 2013. Additionally, a supplementary molecular identification is provided through the sequencing of three non-overlapping loci of mitochondrial DNA and one locus of the 18S small subunit ribosomal RNA (18S) gene. All the taxonomic features of the I. similisi oocysts shed by S. aurantiirostris were equivalent to those originally described from Saltator similis d'Orbigny & Lafresnaye, 1837. The new sequenced loci were identical, or showed 99.9% similarity, to the samples of I. similisi from S. similis and S. aurantiirostris, confirming the same species from both hosts. Lastly, I. similisi is estimated as a junior synonym of Isospora formarum McQuistion & Capparella, 1992, due to the morphological similarities and wide distribution of its hosts in the Neotropical region. Therefore, this study encourages future taxonomic inquiries into I. similisi collected from other Saltator spp. in order to establish this synonymization of I. formarum with I. similisi, and hence, its wide distribution and dispersion in the Neotropical region, including across the Andes mountains.