Prior studies have demonstrated that individuals without health insurance are less likely to have a usual source of health care and receive preventive services including cancer screening and are more likely to be diagnosed at late stages of cancer. To examine the potential impact of health care reform on stage at diagnosis, we analyzed the relationship between stage at diagnosis and insurance status for patients who were nearly elderly (55-64 years old) and younger elderly (65-74 years old). We examined patients diagnosed with 8 common cancers from January 1, 2005, to December 31, 2007, using data from the National Cancer Database, a hospital-based cancer registry jointly sponsored by the American Cancer Society and the American College of Surgeons, which includes approximately 70% of all malignant cancers in the United States treated at 1400 facilities throughout the United States. Cancer site-specific multivariable log binomial models were used to generate risk ratio (RR) and 95% confidence interval (CI) estimates for advanced stage of disease at diagnosis (stage III or IV vs stage I) by insurance category, controlling for age, race/ethnicity, and area level education. The final analytic cohort contained 843,177 patients. For each cancer site, uninsured and Medicaid-insured patients had the highest proportion of American Joint Committee on Cancer stages III and IV cancers at diagnosis, and those with private insurance and Medicare plus supplemental insurance the lowest. Risk ratios (95% CI) for uninsured patients compared with privately insured patients were 1.75 (1.64-1.86) for prostate, 1.12 (1.11-1.14) for lung/bronchus, 2.08 (1.98-2.17) for breast, 1.25 (1.22-1.27) for colorectal, 1.51 (1.40-1.64) for uterine corpus, 1.91 (1.73-2.12) for urinary bladder, 1.80 (1.62-2.01) for melanoma, and 1.37 (1.24-1.51) for thyroid cancers. Lower RRs (95% CI) observed for patients with Medicare coverage alone were 1.23 (1.17-1.29) for prostate, 1.05 (1.03-1.06) for lung/bronchus, 1.41 (1.33-1.48) for breast, 1.08 (1.05-1.10) for colorectal, 1.20 (1.11-1.31) for uterine corpus, 1.54 (1.40-1.70) for urinary bladder, 1.13 (1.01-1.26) for melanoma, and 1.10 (1.01-1.21) for thyroid. In contrast, there was no significant difference between RRs of late-stage diagnosis for any cancer site for patients insured by Medicare Advantage programs. If health care reform extends coverage to a large proportion of adults who are currently uninsured and provides benefits equal to or better than Medicare coverage, the proportion of patients diagnosed with late-stage cancer is likely to decrease, particularly in subpopulations with low rates of coverage.