A new species of Pilosocereus subg. Gounellea, P. frewenii, is described and illustrated for the first time. It is a dwarf, geographically disjunct relative of P. gounellei and, in contrast to other members of its subgenus, occurs in dense dry forest (on limestone rock outcrops) in an area situated between the Atlantic Forest and savanna (cerrado) biomes, far distant from the caatinga. Its phytogeographical significance is discussed and conservation status assessed as Critically Endangered (CR).