AbstractSchistosomiasis is a parasitic disease that affects millions of people in 78 countries, where it is held responsible for considerable morbidity and mortality. It is caused by a blood fluke, which provokes an immunological response to hundreds of its antigens. This induces multi-organ pathology through the formation of tissue granulomata or circulating immune complexes. In addition, it is amyloidogenic and carcinogenic, through the interaction of immunological perturbation with confounding metabolic and genetic factors. The primary targets of schistosomiasis are urinary and hepatointestinal.The lower urinary tract is mainly affected in S. haematobium infection, and may lead to chronic pyelonephritis and/or obstructive nephropathy. The colon and liver are the targets of S. mansoni and S. japonicum infection, leading to hepatic fibrosis, portal hypertension, and liver failure. S. mansoni may also lead to immune complex glomerulonephritis, which is discussed elsewhere. Both S. haematobium and S. mansoni ova may be carried with the venous circulation to the lungs, where they provoke granulomatous and immune-mediated endothelial injury leading to cor-pulmonale. Ova may be subsequently carried with the arterial circulation to form ‘metastatic’ granulomas in other tissues, notably the brain (S. japonicum), spinal cord (S. haematobium), skin, conjunctiva, and genital organs.Schistosomiasis is preventable. World Health Organization programmes have successfully eradicated or reduced the incidence of infection in many countries, particularly Egypt and China. Prevention strategies include health education, raising hygiene standards, and interruption of the parasite’s life cycle by snail control and mass treatment. The search for a vaccine continues. Effective antiparasitic treatment is now possible with high elimination rates. Available agents include praziquantel and artemether for all species, metrifonate for S. haematobium, and oxamniquine for S. mansoni. Successful outcome correlates with early intervention, before fibrosis has occurred.