Many rodent renal and bladder carcinogens rely upon epigenetic mechanisms of carcinogenesis; such mechanisms are likely to influence the spectrum of urinary tract tumors observed in control and treated animals. This is reflected in several features of chemically induced rodent urinary tract neoplasms, including a low overall tumor incidence, an increased prevalence of urinary tract tumors in rats compared to mice and males compared to females, the tendency for epithelial tumors to predominate over nonepithelial types, and demonstrated links to chronic progressive nephropathy and urolithiasis. Such tendencies are also characteristic of spontaneous urinary tract tumors in rodents. Data to support these observations can be derived from large historical databases such as the Toxicology Data Management System, maintained by National Toxicology Program.