Genetic differentiation between populations of teak (Tectona grandis (L.)) was examined in 9 quantitative characters and 10 allozyme loci. Large differences between populations were revealed in the quantitative traits. Regional patterns were revealed by multivariate analysis of the data, but there were also substantial variation within ecological-geographical defined regions. The differentiation between provenances from Laos were found to be less than the variation within Thailand, West India and Indonesia. A much less pronounced differentiation between populations was found in allozyme markers. The fixation index (F_ST) was only 4%, and no clear geographical pattern was found in the allozyme data. However, some differences were found in the level of diversity. An assignment procedure based on allozyme markers did not prove efficient in differentiating between populations, but this was probably a result of the low F_ST value. The larger differentiation between populations in morphological traits than in allozyme markers is probably a result of adaptation through natural selection and, possibly, a higher mutation rate in quantitative traits than in allozyme loci. Similar result have been found in other studies of forest trees.