Gustavia stenoloba (Lecythidaceae) is described, illustrated, and proposed as a new species, so far known only from the humid forests of the Magdalena Valley in the departments of Antioquia, Boyacá, and Santander in Colombia. Its morphology and relationships with other similar species, such as G. longifolia and G. acuminata are discussed and a preliminary conservation status is proposed according to IUCN criteria.