Karyotypes of 18 rodent species collected in various localities in Thailand were analysed as part of an epidemiological survey of the region using conventional cytogenetic techniques. The aim was to re-assess the reliability of karyotype-based diagnoses of Thai rodents using an updated taxonomic framework. The species examined include Menetes berdmorei (Sciuridae), Mus caroli, Mus cervicolor and Mus cookii, Hapalomys delacouri, Chiropodomys gliroides, as well as several representatives of most of the lineages of the Rattini tribe, that is Rattus exulans, Rattus losea, Rattus tanezumi, Leopoldamys edwardsi, Leopoldamys neilli, Maxomys surifer, Niviventer fulvescens, Berylmys berdmorei, Berylmys bowersi, Bandicota indica and Bandicota savilei (Muridae). The first descriptions of G- and/or C-banding karyotypes are provided for several of these, that is, B. savilei, L. edwardsi, M. surifer, B. berdmorei, B. bowersi, N. fulvescens and H. delacouri. Although largely in agreement with available data, our findings on chromosome morphology differ slightly from those published for L. edwardsi, M. surifer, B. savilei and the two Berylmys species, B. berdmorei and B. bowersi. In addition, we document the novel finding of B-chromosomes in the genera Berylmys, Bandicota and the emblematic Mus. Importantly, few species-specific chromosomal characteristic could be identified within most of the genera investigated in our study and, in contrast to previous claims, the usefulness of karyotypes for diagnosing these Asian murid species appears to be limited.