We report our observation of an adult solitary eagle (Buteogallus solitarius) in northeastern Mexico, in the Sierra del Abra Tanchipa Biosphere Reserve, on 18 October 2019. We took photographs of the solitary eagle for identification and then reviewed available records of its distribution in Mexico from different information sources. Recent sightings of the solitary eagle are very rare in Mexico, and our observation in northeastern Mexico is noteworthy considering (1) the rarity of the species and (2) that our sighting was outside of its known distribution.