Wolbachia symbionts are obligate intracellular bacteria that cause host reproductive alterations in many arthropods and filarial nematodes. We identified Wolbachia symbionts in the cliff swallow bug (Oeciacus vicarious Horvath) and the human bed bug (Cimex lectularius L.) (Hemiptera: Cimicidae) by polymerase chain reaction (PCR) amplification and sequencing using Wolbachia-specific 16S rDNA and FtsZ primers. Phylogenetic analyses using Bayesian, maximum likelihood, and maximum parsimony algorithms indicated, with strong support, that (1) Wolbachia infections in these two cimicid hosts form a monophyletic group, and (2) the Wolbachia strains detected belong to the F clade, previously associated with termites, weevils, and filarial nematodes.