Existing taxonomic studies of Reticulitermes spp. (Isoptera: Rhinotermitidae) from California provide information on only two described species: Reticulitermes hesperus Banks and Reticulitermes tibialis Banks. However, while conducting a genetic evaluation of the genus from North America, we find evidence of species that cannot be identified morphologically with existing information. We also update more current information about other species detected during our investigations, including the positive identification of R. flavipes from California. Therefore, we have conducted a molecular genetics study involving DNA sequencing of a portion of the mitochondrial DNA (mtDNA) 16S gene to determine the extent of genetic variation within Reticulitermes from California. We analyzed 94 samples. Twenty-five nucleotide sites were variable in R. hesperus, and 19 mtDNA haplotypes were observed in the 428-bp mtDNA sequence. Fourteen haplotypes (37%) occurred only once, whereas the most common haplotypes, HE4 and HE9, each occurred in 18% of the samples. Although some haplotypes were found to have a broad geographical range across the state, some were restricted to the southern region, as were all samples identified as R. tibialis. Twelve haplotypes of an undescribed western species, R. n. sp. ‘R. okanaganensis,’ were found, and its distribution throughout the state is discussed. Additionally, genetic evidence of two additional undescribed Reticulitermes species from southern California is presented.