Differences in allometric relationships of understorey saplings (60-300 cm tall) between nine common shade-tolerant species of sub-canopy, canopy and emergent trees were examined in an old-growth foothill rain forest in West Sumatra, Indonesia. Interspecific variation was found in the intercept of the regression line between logarithmic dimensions but not in the slope. Detected interspecifc differences could be interpreted as a result of a trade-off between height growth (for future exploitation of better-lit conditions at higher levels in the canopy) and leaf area extension (for current exploitation of poor light nearer the base of the canopy). Saplings of emergent Swintonia schwenkii Teijsm, and Binn. ex Hook. f. favoured height growth rather than expansion of assimilative area. Trends of interspecific differences in sapling allometry in tropical rain forest were similar to those in warm-temperate forest. Tropical saplings had more slender trunks and greater total leaf area at a given height than warm-temperate saplings, but dry weight proportions among organs were similar. We hypothesize that the advantage of maintaining assimilative area in present height is diminished in a habitat with higher growth rate and/or steeper vertical light gradient such as in tropical forest.