The snake Mastigodryas dorsalis (Bocourt, 1890) is generally considered absent from Mexico, but a few sources indicate otherwise. Herein we resolve this issue by re-examining a historical specimen and by reporting new records for M. dorsalis in Chiapas, Mexico. These records extend the known distribution of the species 87 km northwest of the nearest pre-existing record in Guatemala. Additionally, based on these new records and an exhaustive literature review, we present an updated distribution for the species and revise its known elevational range to 300–2110 m. A complete Spanish translation of this paper is available in the Supplemental Data. Una traducción completa al español de este artículo está disponible en los Datos Suplementarios.