The Formosan subterranean termite, Coptotermes formosanus Shiraki, has invaded many parts of the world including the Pacific Rim and the United States. Native to China and the South Pacific, C. formosanus was probably transported to the Hawaiian Islands around 1907 or earlier. The transport of C. formosanus was probably linked to the sandal wood trade by China or the extensive numbers of immigrants from Japan and China. This termite causes immense damage as an agricultural and urban pest species. We are investigating the colony structure of C. formosanus populations from the islands of Kauai and Maui, Hawaii. Subterranean termite colonies have a complex social organization; colonies can be headed by a single pair of reproductives or by multiple neotenic reproductives with variable degrees of inbreeding. Since subterranean termite colonies cannot be directly observed, information about the colony breeding structure has to be indirectly inferred by molecular methods. In this study we use microsatellite genotyping to describe colony identity, reproductive structure, relatedness and inbreeding. We genotyped 20 workers per colony from 22 colonies on Kauai and 18 colonies on Maui at eight microsatellite loci. We will infer the breeding system of each colony from the distribution of genotypes among the workers, the coefficients of relatedness as well as F-statistics in comparison to computer simulations. Results will be compared to other introduced populations of C. formosanus.