Abstract Trechus breuili Jeannel 1913, a hypogean species from the southern Iberian peninsula, is redescribed and a new distribution reported. Following a detailed study of the aedeagus (conformation of the inner sac and the apical lamina asymmetrically curved to the left), the species is assigned to the T. martinezi-lineage (sensu Ortuno and Arillo), which comprises a group of species showing strong biogeographical coherence (southwestern Mediterranean region).