Schistosomiasis, the second most common parasitic infection of humans after malaria, is responsible for approximately 200 million human infections and 200,000 deaths each year.65 and 132 This parasitic infection is endemic in many less developed countries in tropical and subtropical regions of Africa, Asia, the Caribbean, and South America. As a result of travel and immigration, an estimated 400,000 or more people with schistosomiasis live in the United States.133 Schistosomiasis is caused by trematode blood flukes of the genus Schistosoma. Five species are responsible for human infections and numerous others only infect animals. The species that infect humans include Schistosoma haematobium, S. mansoni, S. japonicum, S. intercalatum, and S. mekongi. Chronic infections with all Schistosoma species with the exception of S. haematobium can cause significant morbidity and mortality as a result of granuloma formation in the intestine and liver. The resulting hepatic fibrosis can lead to portal hypertension that eventually can be complicated by splenomegaly, esophageal varices, hematemesis, and death. S. haematobium primarily affects the urinary tract, resulting in chronic inflammation of the bladder, ureteral obstruction leading to hydronephrosis, stone formation, and urinary tract infections that can be complicated by gram-negative septicemia. 38 Although there have been reports of liver disease due to S. haematobium, 3 these are extremely uncommon. Because the focus of this issue is on the liver, infection due to S. haematobium is not reviewed. S. mansoni and S. japonicum have been most intensely studied, and this article reflects available data on these two species unless otherwise indicated.