The objective of the present study was to examine the phylogenetic position of Setaria cervi based on sequences of mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. A fragment of the cox1 gene from two morphologically identified S. cervi collected from red deer (Cervus elaphus) from Italy were amplified, sequenced, and compared with corresponding sequences of other filarioid nematode species. Phylogenetic studies using Bayesian analysis revealed S. cervi as monophyletic with other Setaria species, confirming S. cervi as a member of the Setaria genus. S. cervi appeared to be sister species to Setaria labiatopapillosa and Setaria digitata. Setaria tundra and Setaria equina, the other two Setaria species presented in the Italian fauna, formed a sister group to the clade consisting of S. cervi, S. labiatopapillosa, and S. digitata. In addition to phylogenetic clarification, our study is the first molecular identification of S. cervi, which may be useful for further molecular identification and differentiation of this filarial worm from other filarioid nematode species, especially in the earlier developmental stages of its life cycle.