We document six cases in which tissues were invaded by Enterobius vermicularis. These cases illustrate several mechanisms whereby the worms form granulomata in ectopic sites. In three cases, the worms passed through pre-existing breaches in the intestinal mucosa. In one case, a gravid worm migrated via the female genital tract to ther peritoneal cavity. In two other cases, male worms were found on the outer surface of the intestine, suggesting active penetration of the intestinal wall.