Based on over 400 collections of smut fungi (Ustilaginales and Tilletiales, Basidiomycetes) from Costa Rica and literature review, a checklist of Costa Rican smuts is published for the first time. It presents fifty-two smut species across eighteen genera, including keys, synonyms, morphological descriptions, host species, distributions, and necessary taxonomic discussions. Many species are recorded for Costa Rica for the first time, with sixteen host plants previously unknown for the respective smut species. Special emphasis is placed on the morphology of the sori, the development of the teliospores, and their germination. Numerous line drawings illustrate many morphological details and germinations for the first time. Several new genera, species, and combinations found among Costa Rican smuts are briefly described, as they have been published in detail elsewhere. The name Ustilago eriochloae Ling, based on a misidentified Costa Rican specimen of Ustilago schroeteriana Hennings, is reduced to synonymy. This work provides a comprehensive overview of smut fungi in Costa Rica, enhancing the understanding of their diversity and taxonomy in the region.
