Schistosomal obstructive uropathy was studied by clinical, laboratory epidemiologic and pathologic analysis in 155 Egyptian patients treated surgically. Most patients were men; rural farmers or laborers. All had severe urinary schistosomiasis with heavy burdens of Schistosoma haematobium eggs in their urinary tracts. Schistosomal incomplete ureteral stenosis and schistosomal stenosis with ureterolithiasis were the most important obstructive lesions; these lesions were symmetrical and most frequent in the interstitial ureters decreasing proximally. The pathogenesis of these lesions is dependent upon focal destruction of ureteral muscle. The ureteral lesions proximal and consequent to schistosomal obstructive lesions are hydroureters resulting from active dilatation (due to increased hydrostatic pressure consequent to obstruction) and passive dilatation (due to loss of circular muscle action in sites of oviposition in the proximal ureter). Various combinations of these lesions with superimposed effects of bacterial infection and ureterolithiasis produce the spectrum of ureteral lesions attributable to urinary schistosomiasis.