Forty-eight species of Medinilla are now known from Borneo, 28 of which are described as new. At least 20 taxa are known only from one to three collections. Eleven species groups have been recognized and defined. A more thorough understanding of the genus awaits further study of Philippine and New Guinea materials. A key to the Bornean species, illustrations of 15 species, and ecological notes are provided. Two previously described species are recorded for the first time for Borneo: Medinilla succulenta (Blume) Blume, and M. pterocaula Blume. One new combination and five reductions have been made. Medinilla tawaensis Merrill is transferred to Catanthera; M. caudatifolia Schwartz and M. hasseltii Blume var. subsessilis Schwartz are reduced to M. crassifolia (Reinw. ex Blume) Blume; M. dajakorum Schwartz is reduced to M. corallina Cogn.; M. borneensis Blume and M. motleyi Hook. f. ex Triana are conspecific with M. macrophylla Blume.