Schistosomiasis affects around 200 million persons in the world despite improved knowledge of its epidemiology and physiopathology and significant therapeutic advances. Reliable diagnosis at present is based on observation of the parasite eggs. Schistosoma mansoni causes hepatointestinal schistosomiasis, and S. haematobium causes genitourinary disease. Other species are less frequently observed. The parasites develop in the intrahepatic blood vessels. The females migrate to different parts of the body to lay their eggs, still in the blood vessels. The eggs of different species are of variable size, but all contain a larva called miracidium and all possess a spur. Precise diagnosis is based on the morphologic characteristics of the eggs. As the eggs block different organs, especially the liver, they cause inflammatory granulomas to form. The different species of schistosomas have different geographic distributions that depend partly on the distribution of their mollusk intermediate hosts. S. mansoni and S. haematobium are present in Africa and S. mansoni is also found in the Americas. The eggs of S. haematobium are present most frequently in the urine, while in other species they are found in the stool. The procedure for collecting and preparing the specimens is described. Rectal biopsies obtained during consultations can be examined immediately if facilities are available, and biopsies may also be taken during surgical procedures. The size, color, shape, shell, and spur of eggs of each species are described, and characteristics peculiar to each are noted.