In Costa Rica, teak (Tectona grandis) is grown for timber and fruit production. Fruits are marketed as seed for sexual reproduction; however, there are no defined parameters available for farmers to grade seeds (fruits) according to its quality. The objective of this research was to determine if seed quality is influenced by fruit size. Teak fruits were harvested in a commercial teak field in Santa Cruz, Guanacaste, and were classified by size as large (external diameter greater than 1,2 cm), and small (external diameter equal or smaller than 1,2 cm).  The relationship between the fruit external diameter (with mesocarp) and the internal diameter (endocarp) was measured in 200 fruits of each class. Seed viability with the tetrazolium test was recorded for four groups of 50 seeds per each fruit size category, as well as number of seeds per fruit. Seed germination was evaluated plastic boxes containing peat moss. Boxes were arranged in a complete randomized design with four replications.  Internal diameters for small and large fruits were 9.4 mm and 10.1 mm, respectively. The overall R² for the relationship between these two variables was 0.40.  The relation outer/inner diameter was greater in large fruits (1,31) than is small fruits (1.24). The average number of seeds per fruit was greater in large fruits (1.9) than in small fruits (1.6), however, there were no differences in seed viability between the two groups, with values of 73 % and 74 %, for small and large fruits, respectively. There was no evidence of a difference in seed germination between large and small fruits.