Sycophaginae is a group of non-pollinating fig wasps considered closely related to the fig pollinators (Agaoninae, Tetrapusiinae, and Kradibiinae) in the most recent phylogenetic analyses. They occur in all tropical regions and are associated with Ficus subgenera Urostigma and Sycomorus . There are six described genera of Sycophaginae, and two are native and confined to the Neotropics, namely Idarnes Walker, 1843 and Anidarnes Bouček, 1993. Genus Idarnes is divided into three morphologically distinct groups that were proven to be monophyletic by recent molecular phylogenetic analyses. In this paper we reviewed the Idarnes incertus species-group and provide detailed morphological descriptions and illustrations for the species belonging to this group. Three previously described species were redescribed: I. brasiliensis (Mayr, 1906) comb. nov. , I. hansoni Bouček, 1993, and I. incertus (Ashmead, 1900). Seventeen new species are described by Farache and Rasplus: I. amacayacuensis sp. n. , I. amazonicus sp. n. , I. americanae sp. n. , I. badiovertex sp. n. , I. brevis sp. n. , I. brunneus sp. n. , I. comptoni sp. n. , I. cremersiae sp. n. , I. dimorphicus sp. n. , I. flavicrus sp. n. , I. flaviventris sp. n. , I. gibberosus sp. n. , I. gordhi sp. n. , I. maximus sp. n. , I. nigriventris sp. n. , I. pseudoflavus sp. n. and I. ramirezi sp. n . We provided keys for the identification of the species as well as for recognising the different species-groups of Idarnes and a closely related genus ( Sycophaga Westwood, 1840). Additionally, phylogenetic relationships among 13 species of the I. incertus species-group were inferred using four molecular markers and discussed in the light of Ficus taxonomy and host specificity.