An updated classification of Polyalthia in Peninsular Malaysia is presented. A synopsis (listing of species with synonymy and typification, and keys to species) is presented for the genera Huberantha, Maasia, Monoon and Polyalthia sensu stricto. One new species (Polyalthia pakdin I.M.Turner & Utteridge sp. nov.) is described and a conservation assessment presented for it. Monoon xanthopetalum Merr. represents a new record for Peninsular Malaysia. Six new lectotypes are designated.