A taxonomic assessment of the microhylid genera Chiasmocleis and Syncope occurring in the Amazon basin and Guiana Shield is presented. Syncope Walker, 1973, is considered a junior synonym of Chiasmocleis Méhelÿ, 1904, based on the monophyly of the group as a unit. To avoid secondary homonymy with Syncope carvalhoi Nelson, 1975 (senior homonym), a replacement name, Chiasmocleis lacrimae, nom. nov., is given to Chiasmocleis carvalhoi Cruz, Caramaschi, and Izecksohn, 1997 (junior homonym). From integrative analyses of morphological, acoustic, and a phylogenetic analysis of three genes (two mitochondrial, 16S: up to 557 bp, COI: up to 658 bp; and one nuclear, tyrosinase: up to 532 bp), we recognize 16 species in the area of study, 13 of which were previously known and three are described as new: Chiasmocleis albopunctata; C. anatipes; C. antenori; C. avilapiresae; C. bassleri; C. carvalhoi; C. devriesi; C. haddadi, sp. nov.; C. hudsoni; C. magnova; C. papachibe, sp. nov.; C. royi, sp. nov.; C. shudikarensis; C. supercilialba; C. tridactyla; C. ventrimaculata. Chiasmocleis jimi Caramaschi and Cruz, 2001, is considered a junior synonym of Chiasmocleis hudsoni Parker, 1940. Species accounts are provided for all 16 species, as is a compilation of available data, including type specimens, type localities, morphological diagnoses, variation, tadpoles (only from literature), advertisement calls (calls of several populations described for the first time), and natural history. Photographs and updated data on geographical distributions, with maps, are also provided. The evolution of some phenotypic traits is studied in light of a phylogeny of the group.