Despite the great importance of Wuchereria bancrofti in causing human lymphatic filariasis, only conventional morphological studies have been completed with adult forms of this filaria. No ultrastructural studies have been carried out, mainly due to the difficulty in obtaining viable parasites from human tissues and the lack of a suitable experimental model or in vitro cultivation. With the recent success in using ultrasound to localize adult worms in living tissues and their surgical recovery from human lymphatic vessels, we show in the present paper the first ultrastructural observations of this filarial form. The cuticle surface analyzed by scanning electron microscopy showed a transversal striated aspect with periodic annulations and many small protuberances irregularly distributed along the filaria. The adults present a specialized cephalic area, with the oral opening surrounded by a circular mouth, papillae, and amphidial opening. Other structures, for example the anal, vulvar, and cloacal opening and spicules, were also observed and are described herein.