For 26 tree species in very dry tropical forest in México, the developmental trends of relationships among trunk diameter, tree height, and crown diameter were inferred from a one-time measurement of dispersed individuals across the size range from saplings to large, mature trees. On hillside sites in this high diversity forest, maximum dimensions were usually <10-m height, 4-m crown diameter, and 0.3-m trunk diameter. The relationship of height to trunk diameter was characterized by an asymptotic, three-parameter model. Crown diameter was a linear function of trunk diameter. The parameter values for both models varied widely among the species. In general, the dispersion among species of the height–crown diameter relationship increased linearly with trunk diameter (up to 0.2 m). Arborescent cacti were distant from other species at all sizes, although they were well modeled using the same equations. Empirical and theoretical features and limitations of the present and previous models, including mechanical buckling and water-stress theories, are considered.