Four new species of the genus Isometrus are described: Isometrus (Reddyanus) bilyi from Australia, I. (R.) petrzelkai from Vietnam and Thailand, I. (R.) problematicus from India and I. (R.) khammamensis from India. Keys are presented to all species of both subgenera of Isometrus. Lectotypes are designated for I. (I.) thurstoni Pocock, 1893 and I. (R.) assamensis Oates, 1888. I. (I.) sankariensis Tikader & Bastawade, 1983 is synonymized with I. (I.) thurstoni Pocock, 1893. First time records include I. (I.) thurstoni Pocock, 1893 from Kerala (India), I. (R.) assamensis Oates, 1888 from Madhya Pradesh and West Bengal (India) and Bangladesh, I. (R.) rachycentrus Pocock, 1899 from Tamil Nadu (India), I. (R.) heimi Vachon, 1976 from New Guinea, I. (R.) kurkai Kovařík, 1997 from Sumatra (Indonesia), Kalimantan and Sarawak (Malaysia), I. (R.) navaiae Kovařík, 1998 from Indonesia and I. (R.) rigidulus Pocock, 1897 from Maharashtra and Rajasthan (India). I. (R.) isadensis Tikader & Bastawade, 1983 from India is considered a nomen dubium.