tAngiostrongylus costaricensis is a parasitic nematode that can cause severe gastrointestinal disease,known as abdominal angiostrongiliasis, in humans. This paper presents the characterization of first-and third-stage larvae and male and female adult worms of A. costaricensis by scanning electron andlight microscopy. Several novel anatomical structures were identified by scanning electron microscopy,including details of the cuticular striations of the spicules in male worms and a protective flap of the cuti-cle covering the vulvar aperture in female worms. Other taxonomic features revealed by light microscopyinclude the gubernaculum and the esophageal–intestinal valve. The use of two microscopy techniquesallowed a detailed characterization of the morphology of this nematode. A number of previously identi-fied taxonomic features, such as the striated nature of the spicules and the lateral alae were confirmed;however, the use of scanning electron microscopy resulted in a reassessment of the correct number ofpapillae distributed around the oral opening and behind the cloacal opening. These observations, in com-bination with light microscopy-based characterization of the gubernaculum and esophageal valves, haveallowed a more detailed description of this nematode taxonomy.