Cymothoa catarinensis sp. nov. collected at Camboriú, Santa Catarina State, Brazil is described. The new species is of small size, has a cephalon that is little immersed in pereonite 1, anterolateral angles of pereonite 1 that reach or surpass the eyes and a pleon that is deeply immersed in pereonite 7. The pleopods of the new species have small, lobular accessory gills projecting from the bases. Cymothoa excisa Perty, 1830, and Cymothoa oestrum (Linnaeus, 1758) are redescribed. Both are of large size (25-35 mm in length). C. excisa has pointed anterolateral margins of pereonite 1 that reach or surpass the eyes. This species also has trilaminate pleopods in the female and bilaminate pleopods in the male. C. oestrum has rounded anterolateral margins of pereonite 1 and no visible eyes. This is the first time the latter species has been reported from Brazil. These three species are compared to four others that have been reported from Brazilian waters, namely: C. liannae Sartor & Pires, 1988; C. brasiliensis, C. gerris and C. ianuarii, all described by Schiödte & Meinert, 1884. A key is provided to aid in the separation of the Brazilian species of Cymothoa.