The genus Peristethium Tiegh. (Loranthaceae) is re-established to comprise five species previously placed in Struthanthus Mart. (P. aequatoris (Kuijt) Kuijt, P. leptostachyum (Kunth) Tiegh., P. lojae (Kuijt) Kuijt, P. polystachyum (Ruiz & Pav.) Kuijt, and the new nomenclatural combination presented here, P. tortistylum (Kuijt) Kuijt). Also included are five species from Cladocolea Tiegh. (P. archeri (A. C. Sm.) Kuijt, P. peruviense (Kuijt) Kuijt, and P. primarium (Kuijt) Kuijt), with two transferred as new nomenclatural combinations herein, P. nitidum (Kuijt) Kuijt and P. roraimense (Steyerm.) Kuijt). Additionally, five new species are described and illustrated (P. attenuatum Kuijt, P. colombianum Kuijt, P. confertiflorum Kuijt, P. lamprophyllum Kuijt, and P. palandense Kuijt). The genus Peristethium thus consists of 15 species and a key is provided for the genus. It is characterized by pairs of conspicuous, often caducous, chaffy scale leaves at the base of the mostly determinate inflorescences, and by lateral inflorescence units that are triads and/or ebracteolate single flowers called monads (in one case, partly pentads). Some species have bisexual flowers while others are dioecious; flowers are either tetramerous or hexamerous, and one pentamerous species is included (P. nitidum). The minute anthers are sessile or nearly so, placed far above the middle of the petals. Geographically, the genus reaches from northern Bolivia to Costa Rica, with two rare, narrow endemics on Mt. Roraima in Venezuela and the Pakaraima Mountains.