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Summary The shape of the teeth and their sex-dependent dimorphic expression in three species of Costa Rican plethodontids ( Bolitoglossa subpalmata, Oedipina uniformis and Nototriton abscondens ) were studied using light microscopy and scanning electron microscopy. The teeth of the vomerine tooth patches are about one third larger than the teeth of the jaws in B. subpalmata and O. uniformis , whereas all teeth of N. abscondens are of about uniform size. The occurrence of bicuspid tooth germs in the fetus proves that primary teeth are bicuspid in these directly developing plethodontids. Females possess only bicuspid teeth consisting of a pedicel and a crown, as is considered characteristic for urodeles after metamorphosis. Adult males possess conical monocuspid teeth on the premaxillary. These teeth — which are similar to the typical late larval tooth of salamanders presenting a larval stage — are about twice as big as the neighbouring bicuspid maxillary teeth. N. abscondens males possess some monocuspid teeth and teeth of aberrant shapes on the premaxillary and the maxillaries. A tendency to build more monocuspid teeth in the premaxillary region than in the maxillary region can be observed in this species. We suppose that different degrees of sensitivity to androgens in each section of the dental lamina of the upper jaw cause the secondary occurrence of conical monocuspid teeth predominantly on the premaxillary section.