In the second article of this series, we discuss the diagnosis and treatment of some important intestinal nematodes. Common parasites discussed in detail include Ascaris lumbricoides, Trichuris trichiura, hookworm, and Enterobius vermicularis (pinworm). In addition, Strongyloides stercoralis has emerged as an important pathogen in immunocompromised patients, and Capillaria philippinensis is now recognized as an important cause of diarrhea in Asia. Finally, anisakiasis and other illnesses due to parasitic nematodes are discussed.