BACKGROUND. The National Cancer Data Base (NCDB), a joint project of the Commission on Cancer of the American College of Surgeons and the American Cancer Society, is a cancer management and outcomes data base for health care organizations. It provides a comparative summary of patient care that is used by participating hospitals and communities for self-assessment. This article describes the most current (1995) data. METHODS. Since 1989, 7 calls for data have been issued, yielding a total of 5,558,389 cancer patient reports for the years 1985-1995. A total of 1849 hospital cancer registries have participated in at least 1 of the calls for data. RESULTS. One thousand one hundred and fourteen hospitals from 50 states and the District of Columbia reported 655,627 eases for the diagnosis year 1995. The hospitals represented a wide range of sizes (187 [16.8%1 with 1000+ cases annually, 405 [36.4%] with 500-999 cases annually, 255 [22.9%] with 300-499 cases annually, 211 [18.9%] with 100-299 cases annually, and 56 [5%] with < 100 cases annually) and types (21 [1.9%] National Cancer Institute [NCI]-recognized cancer centers, 119 [10.7%] government hospitals, 102 [9.2%] teaching hospitals, 256 [23.0%] large community hospitals, 297 [26.7%] medium/small community hospitals, and 257 [23.1%] nongovernmental hospitals without approval status from the Commission on Cancer or NCI recognition). Remarkably similar distributions of cases by primary site and age were reported from each of six U.S. geographic regions. In addition, within each of these six regions, the eases were reported from a wide range of income strata and ethnicities. For several states, relatively few cancer cases were reported. For several examples of relatively rare patient and tumor groups, all reported cases between 1985-1995 included potentially useful quantities of patients in whom further study of such special groups was warranted. CONCLUSIONS. The authors conclude that the reported cases most likely are representative at the regional (but not state) level of cancer patients diagnosed and treated at U.S. hospitals with regard to types of cancer and ages of the patients. They conclude further that cancer reporting may be quite diverse within each region with regard to other known patient and reporting institution characteristics.