The Transphlebotomus subgenus has been drawing attention in last decade due to the uncertain vector capacity and cryptic life history of the group. During a 2015 entomological survey, Phlebotomine flies were collected in western locations of Slovenia, with a total of 22 specimens of the Transphlebotomus subgenus collected. In addition to morphological identifications, we confirmed the presence of Phlebotomus mascittii Grassi, 1908 (Diptera: Psychodidae) by nucleotide sequences of the mitochondrial cytochrome b gene. During the study, we found that P. mascittii is most abundant in the area of coastal–karst region of Slovenia, while in rare occasions can also be collected in Northeastern part of the country, near the Austrian border. Vector competence of P. mascitii, like all other member species of the Transphlebotomus subgenus, is unclear, but potential to transmit Leishmania (Kinetoplastida: Trypanosomatidae) pathogens or phleboviruses is strongly suspected.