We summarize the bird species known from the Tres Marías Islands, off the coast of Nayarit, western Mexico, tabulating the sources for the occurrence of each species by island. We report records of 48 species new to the archipelago and/or specific islands on the basis of our field work since 2002 and a review of published literature, museum specimens, and others’ observations. These bring the number of species known from the Tres Marías Islands to 176, of which 5 represent introductions and about 46 others are known or likely to breed; about 24 of the 46 represent endemic subspecies. All resident species recorded historically still survive on at least one of the islands. In spite of our recent field work, the precise status of many species by island remains to be clarified.