Schistosoma haematobium infection is a common occurrence in Africa and the Middle East and is the world's leading cause of hematuria. Since more North Americans are venturing into endemic areas and more residents of endemic areas are seeking medical care in North America, pathologists must be able not only to diagnose urinary schistosomiasis but also to provide advice as to further therapy. These endeavors mandate knowledge of the pathobiologic features of the disease. The severity and frequency of the sequelae of urinary schistosomiasis (hydroureter, hydronephrosis, bladder ulcer, and polyposis) and of its complications (bacterial urinary tract infection, renal failure, urothelial cancers) depend on the intensity of infection, i.e., worm burden and tissue egg burden, and the duration of infection. Significant differences in gross and microscopic morphology, clinical laboratory findings, and optimal mode of treatment exist between active (during active egg deposition) and inactive (after cessation of oviposition) disease. Moreover, nearly half of the severe sequelae and complications occur during the inactive phase of the disease, when diagnosis is most difficult. The manifestations of this disease are manifold and complex, and firm understanding of the pathobiologic features is necessary if pathologists are to understand their role in the direction of treatment.