pinworm, roundworm, Enterobius vermicularis, worldwide in distribution and the most common source of worm infestation of humans in the United States. Children are more commonly infested than adults. Adult pinworms inhabit and mate in the cecum of the large intestine and adjacent areas. When mature females become gravid they migrate down the colon and out onto the skin around the anus where they lay about 10,000 eggs and then die. Such movements cause intense anal itching. The eggs are infective within a few hours and are easily spread by the hands to the mouth, most often through touching contaminated household objects or food supplies. If infective eggs are swallowed the young worms hatch in the duodenum and migrate to the cecum. Development from ingested egg to gravid female requires 2 months. The most prominent symptom of the disease resulting from pinworm infestation, called enterobiasis, is anal itching, particularly at night; restlessness and insomnia are common, and sometimes gastrointestinal symptoms such as abdominal pain, nausea, and diarrhea, are also present. Since reinfection is a major problem, enterobiasis is treated by the following of strict hygienic measures, including careful cleansing of hands, body, and bed linens. Often, all members of the household must be treated for the disease. Pinworms are classified in the phylum Nematoda, order Oxyuroidea, family Oxyuridae.