In this account the genus Trichosanthes L. has 20 species occurring in Thailand, Cambodia, Laos and Vietnam. Since the treatments in Flore du Cambodge, du Laos et du Viêtnam (Keraudren-Aymonin 1975; 10 species), and in Flora of Thailand (De Wilde & Duyfjes 2008a; 17 species) more knowledge by fieldwork in Thailand has become available resulting in the inclusion for Thailand of the taxa T. baviensis Gagnep., T. pedata Merr. & Chun, T. tricuspidata Lour. subsp. rotundata W.J.de Wilde & Duyfjes. For Cambodia, Laos and Vietnam of the species T. dunniana H.Lév., T. erosa Duyfjes & Pruesapan var. erosa, T. inthanonensis Duyfjes & Pruesapan, T. fissibracteata C.Y.Cheng & C.H.Yueh, T. tricuspidata Lour. subsp. rotundata W.J.de Wilde & Duyfjes, and T. truncata C.B.Clarke. Two keys to the species are presented, one for male flowering specimens, and one for fruiting specimens, as well as for each species literature references, distribution and occasional other information.