Plerocercoid should not be confused with Sparganum. The scolex of plerocercoid has a bothrium or bothrial slit but there is no true scolex in sparganum. Plerocercoid is a developmental stage of an animal tapeworm， Genus Spirometra. Sparganum is another generic name of a pseudophyllidean cestode. Plerocercoid causes benign plerocercoidosis and sparganum causes “malignant sparganosis”. Plerocercoidosis is a parasitic zoonosis which can be food-borne， water-borne， contact-borne or mother-borne. During the past 20 years， there has been significant progress in studies of human plerocercoidosis and sparganosis， especially the former. Spirometra erinacei-europiea plerocercoidosis and sparganosis prolifera distributed mainly in East Asia. Spirometra mansonoides plerocercoidosis has been reported from the USA． Up to the present， approximately 1 400 cases of plerocercoidosis were reported from China, Japan, Korea, USA and Thailand, and at least 16 well-documented cases of human proliferating sparganosis were reported worldwide （in Japan, China, Thailand, USA, Paraguay, Venezuela, and the Philippines). The life cycle of Sparganum is unknown. For plerocercoid, human being acts as a dead-end hosts， copepod and frogs serve as intermediate hosts， and snakes and carnivorous animals are its paratenic hosts. This review summarizes the research progresss on aetiology and pathogenesis of human plerocercoidosis and sparganosis. The second part （in press) will be concentrated on their pathology, clinical manifesta-tions， diagnosis， treatment，epidemiology， control and prevention.