A taxonomic study on the South American dwarf boas of the genus Tropidophis revealed the existence of two new species in the Atlantic Forest biome. As a result, we recognize five mainland species, three in the Atlantic Forest and two in northwestern South America. Based on general distribution and morphological orientation, the type locality of T. paucisquamis is restricted to Estação Biológica de Boracéia (EBB), municipality of Salesópolis, state of São Paulo, Brazil; furthermore, a lectotype for T. taczanowskyi is designated. We provide data on the hemipenial morphology of two South American Tropidophis, showing that the quadrifurcate condition described for West Indian taxa also occurs in mainland congeners. The distributions of the three Atlantic Forest species are congruent with patterns of diversification of other vertebrate taxa associated with cold climates prevalent at high elevations. Refugial isolation and riverine barriers may account for such speciation events.