The diving beetle genus Microdytes J. Balfour-Browne, 1946 in Thailand, Laos, and Cambodia is reviewed, and five new species are described: Microdytes eliasi Wewalka & Okada, sp. nov. (Thailand, Cambodia), M. jeenthongi Okada & Wewalka, sp. nov. (Thailand), M. maximiliani Wewalka & Okada, sp. nov. (Laos, China), M. sekaensis Okada & Wewalka, sp. nov. (Thailand, Laos), M. ubonensis Okada & Wewalka, sp. nov. (Thailand, Laos). Two species are the first country records: M. balkei Wewalka, 1997 (Laos, Cambodia) and M. wewalkai Bian & Ji, 2009 (Laos). For 12 and 8 species, the first provincial records from Thailand and Laos, respectively, are given. A checklist, a key to the 25 known Microdytes species from these countries, and habitus images and illustrations of diagnostic characters are provided. Distribution maps of the recorded species are presented, and species distribution patterns are also briefly discussed. [ABSTRACT FROM AUTHOR]