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We studied differences in age, longevity, and sexual maturity in island and mainland populations of the neotropical toad Rhinella ornata to assess how changes in sexual characteristics relate to evolution of insular dwarfism. Here we tested the hypothesis that effects of the island rule results in earlier sexual maturity. We sampled males from three insular (Ilha Grande, Ilha da Marambaia and Ilha de Itacuruçá) and four adjacent mainland sites in the state of Rio de Janeiro, Brazil. Age, estimated by skeletochronology, was contrasted to sexual classes defined based on observation of secondary sexual characters (i.e., nuptial excrescences). Individuals reached sexual maturity after one year and longevity was estimated at an age to be up to four years. The presence of nuptial excrescences was influenced by age and growth rate and varied between populations. Individuals from Ilha Grande reached reproductive maturity at smaller sizes than their co-specifics on the mainland. Age and longevity of R. ornata were in agreement with the data of other tropical frog species. [ABSTRACT FROM AUTHOR]