We present a reinterpretation of the unique group of painted glyphs of the Plaza de los Glifos, in the La Ventilla residential area (ca. A.D. 300–450) situated in the ancient central Mexican metropolis of Teotihuacan. Based on a careful review of previous interpretations of the glyphic La Ventilla floor, the writing system, and the possible language(s) of Teotihuacan, we suggest that the majority of the 42 glyphs are not references to toponyms or titles, but are related to disease-causing entities and curing rituals. Crucial to this proposal is the identification of two glyphic representations of a ‘deer-snake,’ a supernatural creature closely tied to diseases and ailments known throughout most of Mesoamerica and beyond, before and after the conquest. We further argue that contemporary and colonial concepts and practices concerning illness and curing offer ways of understanding several other glyphs from La Ventilla and may serve to account for the unusual placement of the signs.