A revised classification of the species of Cyathocalyx (Annonaceae) occurring in western Malesia (Peninsular Malaysia, Sumatra, and Borneo) is presented, with distribution maps. Fifteen species are recognized, including two that are newly described from Borneo ( C. angustipetalus and C. magnifructus), which are illustrated. Several important nomenclatural changes are validated, including the elevation of Drepananthus carinatus var. deltoideus to specific rank as C. deltoideus, and the transfer of the name Parartabotrys hexagynus to Cyathocalyx as C. hexagynus. Other notable nomenclatural changes include the reduction of the name C. scortechinii to synonymy with C. pubescens. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 152, 513–532. [ABSTRACT FROM AUTHOR]