Seventy-one isolines of Anopheles campestris-like were established from wild-caught females collected from human-biting and animal-biting traps at 12 locations in Thailand. All isolines had an average branch summation of seta 2-VI pupal skins ranging from 20.3-30.0 branches, which is in the range of An. campestris (17-58 branches). They showed three different karyotypes based on the amount of extra heterochromatin in the sex chromosomes, namely Forms B (X2, Y2), E (X1, X2, X3, Y5) and a new karyotypic Form F (X2, X3, Y6). Form B has been found only in Chaing Mai and Kamphaeng Phet populations, while Forms E and F are widely distributed throughout the species range. Genetic crosses between the 12 isolines, which were arbitrarily selected as representatives of An. campestris-like Forms B, E and F, revealed genetic compatibility that provided viable progeny through F2 generations, suggesting a conspecific nature of these karyotypic forms. These results are supported by the very low intraspecies variation (genetic distance < 0.005) of ITS2, COI and COII from genomic DNA of the three karyotypic forms.