Historical control tumor data are useful in the interpretation of long-term rodent carcinogenicity bioassays, especially to assess the occurrence of rare tumors and marginally increased tumor incidences. The major prerequisites to compare historical control data with studies under evaluation are the validity and consistency of the respective databases. The RITA (Registry of Industrial Toxicology Animal-data) database for historical data of tumors and pre-neoplastic lesions collects data according to highly standardized procedures including tissue sampling and trimming, histopathology according to internationally harmonized nomenclature and diagnostic criteria, and peer review. All lesions that are entered are unanimously diagnosed according to IARC (Intermational Agency for Research on Cancer)/WHO criteria. The validity of data is additionally confirmed by a complete peer review performed by a database pathologist. Equivocal diagnoses and selected cases are additionally submitted to a panel of RITA pathologists. In the RITA database, there are currently 10,896 rats from 106 studies with more than 17,604 primary tumors and 16,551 pre-neoplastic lesions. The RITA database for historical control data for Wistar and Sprague Dawley rats as well as for different mouse strains is briefly described. Based upon RITA background data, the survival rate of Wistar rats has been consistent over a period of 10 years. The occurrence of tumor-bearing animals also shows a stable percentage over a decade. Additionally, examples of how historical control data may support carcinogenic risk assessment in cases of rare tumors or marginally increased incidences of tumors and pre-neoplastic lesions are given.