Forty-two different genetic origins of teak (Tectona grandis) comprising 26 open-pollinated families from a clonal seed orchard (CSO) were planted in a replicated trial under 2,500 mm of annual rainfall and no distinct dry season, in 1997, in Sabah, East Malaysia. The trees were measured or scored for various traits at 13, 35, 49, 61, 72, 85, 96, and 106 months after planting. Mortality rate, height (H), diameter at breast height (DBH), volume (V), and fork height (FH) varied strongly among populations and origins. The best population means after 106 months for growth H (21.1 m), DBH (21.1 cm), and V (278 dm(3)) were for the CSO families. Narrow sense heritabilities for the CSO families increased gradually with age but remained lower after 106 months for DBH (h(2)=0.24) and V (h(2)=0.34) than for H (h(2)=0.51) and FH (h(2)=0.56). Overall, the CSO families were also straighter, less forked, and grew more vertically than the native provenance and seed-derived sources. Such differences did not exist for flowering ability, and at 106 months, the great majority of the trees of the various origins had not yet entered the flowering stage. Overall, at 106 months, the phenotypic correlations between the various quantitative and qualitative traits were weak, except between straightness and bending with values higher than 0.50. These findings confirm the usefulness of CSO for teak improvement and demonstrate the beneficial influence of wet tropical conditions on traits of major economical importance for this species.