This article surveys the most important gastrointestinal parasites that affect humans. The modes of acquisition, pathology, epidemiology, diagnosis, and treatment are all briefly examined. Gastrointestinal parasites have become increasingly important in the differential diagnosis of gastrointestinal disease, as a result of a number of circumstances. These circumstances include: increasing travel to developing countries; increased numbers, for one reason or another, of immunocompromised individuals; increased consumption of raw or partially cooked ethnic delicacies; more crowding in day-care centres; increased immigration from developing countries; and an endemic pocket of individuals with certain unhygienic or unsanitary practices.