Relationships between tree height and diameter reflect ecological strategies of tree species, including light competition, mechanical stabilities, water balance, and acquisition and conservation of soil nutrients. In this study, we described the variations among tree species in height-diameter relationships in a tropical dry forest in Ankarafantsika National Park, northwestern Madagascar (annual precipitation of 1,365 mm, with the 6-month-long dry season). In the 15-ha forest monitoring plot in which we had mapped all woody stems with diameter at breast height (DBH) ≥ 5 cm, we examined height of 920 individuals. We used two asymptotic two-parameter models to explore height-diameter relationships for the 22 most dominant tree species, which accounted for 80% of the total basal area. There were wide variations in asymptotic height and the DBH at which half of the asymptotic height is reached. The height-to-diameter ratio, which should be inversely related to the mechanical stability, also widely varied among the 22 species. These differences among species may reflect their differences in light use strategies, and likely covary with functional traits, including wood density, bark thickness, specific leaf area and leaf phenology.