Trematodes are a group of parasitic worms with complex life cycles involving sexual reproduction in vertebrate hosts and asexual reproduction in snail intermediate hosts. Trematodes that infect humans can be divided into 2 general groups, the blood flukes and foodborne flukes. Blood flukes cause schistosomiasis, while foodborne flukes infect the intestine, the liver, or the lungs. Humans acquire these infections by ingesting water or food that has been contaminated with larval forms of the parasite. Manifestations of infection differ according to the specific fluke involved and the organ(s) affected. Long-term sequelae of chronic infections caused by some trematodes include a predisposition to certain malignancies including cancers of the liver and urinary bladder. Most human trematode infections are treated most effectively with praziquantel. Without effective vaccines against any of these infections, prevention of trematodiases is best accomplished by avoiding exposure to water that may be contaminated with larvae and thoroughly cooking fish, crustaceans, and aquatic plants before eating them.