Two Mexican trout taxa are formally described (Oncorhynchus chrysogaster, and O. mykiss nelsoni), but many other congeners have long been informally recognized as likely distinct. For more than two decades, the binational Truchas Mexicanas team searched for and collected trout broadly throughout the Sierra Madre Occidental of Sonora, Chihuahua, Sinaloa and Durango. That fieldwork documented that the native range of the genus extends to the Tropic of Cancer, or ~1000 km S of El Paso, Texas, and indicates that most of Mexico's trout exist as small, isolated populations with very restricted ranges. Genetic studies of Truchas Mexicana's specimens demonstrated that the many distinctive lineages found in Mexico are at least as divergent from one another as are their much more thoroughly-studied relatives in the O. mykiss complex in the Western U.S.A. When an opportunity presented itself to list the many still undescribed Mexican forms in the IUCN Red List, as part of a large project to assess the conservation status of the entire Mexican freshwater fish fauna, the authors rapidly compiled the necessary documentation and submitted the required proposal. Once the proposal was accepted, we then worked with IUCN staff to finalize formal conservation assessments that should be published in the Red List about 1 month after this presentation is given at the 2019 meeting. We hope that this official listing of these 12 mostly undescribed Mexican endemic species, with 3 determined to be Critically Endangered (CR), 5 Endangered (EN), 3 Near Threatened (NT), and one Data Deficient (DD), will call attention to this important biodiversity asset and open doors for much-needed financial support for the conservation actions that are so desperately needed. Meanwhile, work continues on the morphologically difficult diagnoses of the new species and their descriptions.