Moenkhausia hemigrammoides Géry, 1965 was described from Suriname and recently found in the Ariari drainage, part of the Orinoco river basin. Here, we formally report the presence of this species in the Ariari and Inírida drainages of the Guaviare River and present morphological data that complement the original description. Our records of M. hemigrammoides represent the westernmost distribution for this Guianan species in the Amazonas–Orinoco transition zone.