Snakes previously referred to Dendrophidion vinitor from southern Mexico to eastern Panama comprise three sibling species primarily distinguishable by substantial differences in hemipenial morphology and some subtle aspects of color pattern. Dendrophidion vinitor Smith is here restricted to populations from southern Mexico to Belize. Dendrophidion apharocybe new species is distributed from Honduras to Panama, primarily on the Atlantic versant. Dendrophidion crybelum new species is known from middle elevations of the Río Coto Brus valley in southwestern Costa Rica (Pacific versant). Hemipenes of D. vinitor and D. apharocybe are similar in overall shape (short, bulbous) but the former has a highly ornate apex with membranous ridges and an unusual apical boss, whereas D. apharocybe has a largely nude apex strongly inclined toward the sulcate side. Dendrophidion crybelum has an elongate cylindrical hemipenis with a large number of spines. In general, these species are not distinguishable by standard scutellation characters. Hemipenial and other characters suggest that these species are a monophyletic group within Dendrophidion and have the following relationships: (vinitor (apharocybe, crybelum)). Some aspects of the systematics and biogeography of Dendrophidion are discussed. Divergence among the three species is associated with two geological features important to speciation in Middle America, the northern Motagua–Polochíc fault zone (Guatemala–Belize) and the southern Cordillera Talamanca (Costa Rica–Panama).