Dunnifilaria meningica from naturally infectedNeotoma micropus in Mexico were studied by scanning electron microscopy (SEM). The anterior end of adults is surrounded by two pairs of buccal and two pairs of cervical papillae. Two amphidial openings lie near the central mouth opening, surrounded by a thick cuticular ring. The cuticular surface of males and females shows fine transversal striations. At the posterior end of the male is a semicircular cloaca, a large preanal central papilla, two pairs of perianal and two pairs of postanal papillae. The short, strong, and almost equal spicules are rolled plates that end in a knobshaped apex, showing a central groove. In the female, the vulva is located 550 μm from the anterior end. The inconspicuous anus is subterminally situated in the right ventrolateral portion of the posterior end. The anterior tip of the sheathed microfilariae is formed by a cap-like cephalic disk. Cuticular annulations were clearly demonstrated across the body.