Enterobius vermicularis (pinworm) is a tiny helminth that lives in the human cecum. Its prevalence varies widely by region and institutional setting. Prevalence greater than 70 percent has been reported among Asian children in orphanages and adults at autopsy after sudden death. In other settings, pinworm infection is rare. Pinworm is diagnosed relatively easily with a perianal sticky tape test and microscope visualization of eggs or worms. Treatment also is straightforward using pyrantel pamoate, mebendazole, or albendazole once and repeated in 2 weeks. Eggs persist in home or institutional environments and can reinfect. Serious sequelae are not thought to be common, but they can include peritonitis, mesenteric abscess, intestinal perforation, enteric ulceration, enteritis, Meckel diverticulitis, and intussusception from ectopic worm movement. More controversial is the association of pinworm with appendicitis, urinary tract infection, and enuresis; evidence for and against these associations is discussed in the review. Pediatricians encounter pinworm in varying frequencies depending on local environmental dynamics, but this pathogen must be considered on a daily basis worldwide for a wide variety of potential manifestations. Copyright © 2000 by W.B. Saunders Company