Neothaumalea atlanticanew genus, new species (Diptera: Thaumaleidae), is described from the state of Santa Catarina in southern Brazil. This represents the first thaumaleid collected east of the Andes mountain range. The egg, larva, pupa, and both adults are described and illustrated, distribution map presented, and phylogenetic affinities discussed. A key to the genera of South America is also provided.