Stemonoporus Thw. (Dipterocarpaceae), a genus endemic to Sri Lanka, contains as many as 26 species, all but one confined to the perhumid forests of the island. Several species reach 1800 m, the highest altitude recorded for any dipterocarp species in Sri Lanka. We report the first quantitative data on Stemonoporus-domirated stands in the montane zone (1500–1700 m). Stemonoporus cordifolius and 5. rigidus show clear single-species dominance of their respective stands. Stemonoporus gardneri is a co-dominant with Palaquium rubiginosum in its two stands. All Stemonoporus species appear to have a unique geographical and ecological range and no two Stemonoporus species co-exist in our stands.