The genus Monastria Saussure, 1864 includes medium to large sized (40–55 mm) dark brown or black cockroaches found in the understory of the Neotropical Atlantic Forest from the Northeast of Brazil to Paraguay and Argentina. The genus shows evident sexual dimorphism: males are elongated with fully developed wings extending beyond the apex of cerci and females are oval and brachypterous. This study is a revision of the genus with redescription of the three already known species, Monastria biguttata (Thunberg, 1826), Monastria similis (Serville, 1838) and Monastria angulata Saussure, 1864, and description of five new ones, Monastria itubera sp. n. and Monastria itabuna sp. n. from state of Bahia, Monastria cabocla sp. n. from state of Sergipe, Monastria kaingangue sp. n. from state of São Paulo and Monastria sagittata sp. n. from state of Minas Gerais. The morphology of the genus and all species is described in details, including male genitalia. Based on this revision, we proposed a new combination for Hiereoblatta papillosa (Thunberg, 1826) comb. n., excluding it from the genus Monastria. For the first time, the juvenile stages of Monastria are characterized and compared to other genera of Blaberinae of the Atlantic forest. Three determination keys are provided. The two first are aimed at identifying the adults and juvenile stages of the five genera of the Blaberinae radiation endemic to the Atlantic forest, respectively. The third concerns the identification of the species of the genus Monastria. A map indicating the localities where species were sampled is also provided.