Population structure and spatial patterns were examined for four species of canopy dipterocarps (Anisoptera costata, Dipterocarpus alatus, Hopea odorata, Vatica cinerea) in a 50ha plot in seasonal dry evergreen forest at the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Spatial dispersion was assessed with Morisita’s index for quadrat sizes ranging from 61m2 to 25ha; spatial attraction and repulsion between species and size classes were measured with Iwao’s index. Only Vatica had a negative exponential diameter distribution suggesting continuous recruitment. The other species had either normal (Hopea) or irregular diameter distributions with peaks in the large size classes (Anisoptera, Dipterocarpus). All four species were significantly clumped at most quadrat sizes. At the local scale, saplings and poles of Hopea and Anisoptera were negatively associated with adults at quadrat sizes