The complete sequence of the mitochondrial (mt) genome of the assassin bug, Sirtheneaflavipes (Stål), was determined. The circular genome is 15, 961 bp long and contains a standard gene complement, i.e., the large and small ribosomal RNA (rRNA) subunits, 22 transfer RNA (tRNA) genes, 13 protein-coding genes (PCGs), and the 1, 295 bp control region. The nucleotide composition of S. flavipes mt genome is 71.8% AT-rich, reflected in the predominance of AT-rich codons in PCGs. Compared with the other three reduviid species available in complete mt genomes, the genome architecture as well as the nucleotide composition, codon usage, and amino acid composition reflected high similarity. All PCGs use standard initiation codons (ATN); however, ND4L and ND1 started with GTG. Canonical TAA and TAG termination codons are found in nine PCGs, the remaining four (COIII, ND3, ND5, and ND]) have incomplete termination codons. All tRNAs have the typical clover-leaf structure, except the dihydrouridine (DHU) arm of tRNASer(AGN) forms a simple loop as seen in many other metazoans. Secondary structure models of the ribosomal RNA genes of S. flavipes are presented and are similar to those proposed for other insects. The structure of rrnL is more conservative than that of rrnS among sequenced assassin bugs. The monophyly of Reduviidae is highly supported by Bayesian inferences, and the Peiratinae presents a sister position to the Triatominae+ (Salyavatinae + Harpactorinae).