The genus Lactistomyia Melander is revised and include the following eleven species: L. dimidiata (Bellardi); L. hyalia Bezzi; L. insolita Melander; L. lepida sp. n.; L. mammifera Curran; L. minuta sp. n.; L. nigripes Curran; L. paranaensis sp. n.; L. pulchra sp. n.; L. serrata Bezzi and L. tuberculata sp. n.. Except L. dimidiata, all species are described, keyed, male and female terminalia illustrated. Lactistomyia polita Melander, a species from Oriental Region, is not congeneric, is being transferred to Syndyas Loew and receiving a new name: Syndyas melanderi n. nov. The geographical distribution of Lactistomyia is just confirmed for the Neotropical region. Drawings of the female terminalia of L. serrata are supplied for the first time. The phylogenetic relationships of the included species of Lactistomyia, except L. dimidiata, are analysed.