It has been known that urinary diversions juxtaposing the urinary and intestinal tracts lead to increased incidence of secondary malignancies. Although tumorigenesis in ureterosigmoidostomies follows the typical course from adenomas to adenocarcinomas, secondary malignancies arising from isolated intestinal diversions are much more heterogeneous. Research over the last half century has unveiled patterns of incidence and progression, while also uncovering possible mechanisms driving the neoplastic changes. In this review, we summarize the current understanding of these unique tumors, with the hope that the knowledge gained may shed light on the etiologies of other cancers arising from the urinary and intestinal tracts.