Growth rates, maturation sizes and sexual dimorphism in shell morphology (size, globosity and thickness) of Littoraria zebra and L. variegata in a mangrove forest at Malaga Bay (Pacific Coast of Colombia) were studied. The sexes of L. zebra did not show differences in growth rate or maximum size. Minimum sizes at maturity were similar; however, the mean size of mature males was smaller than that of females. Littoraria zebra did not show sexual dimorphism in shell morphology. Females of L. variegata grew almost twice as fast as males, reached larger maximum size and attained sexual maturity at a larger size than males. Females had thinner and more globose shells than males. Littoraria zebra and L. variegata reach sexual maturity at a relatively later stage than other Littorininae species, but they continue growing after maturity. The intersexual pattern of growth, in which males are smaller than females and grow more slowly, is common in Littorininae; however, L. zebra does not seem to follow this pattern. Sexual dimorphism of L. variegata can be explained by the hypothesis of fecundity selection and results from the difference in growth rates. The differences between the two species regarding shell thickness and growth rates are discussed in terms of vertical zonation and predation in the mangrove environment.