BACKGROUND Understanding the joint effects of insurance type and primary care physician density on stage at diagnosis is essential to elucidating the healthcare access and late-stage cancer relationship. PURPOSE To determine if the relationship between primary care physician density and odds of late-stage cancer are modified by insurance type at diagnosis. METHODS Case patients were Ohio adults diagnosed between 1996 and 2008 with cancer of one of the following sites: female breast, cervix, colon/rectum, lung/bronchus, melanoma of the skin, oral cavity and pharynx, or prostate (N=376,425). County-level physician density was obtained from the Ohio Department of Health. Multilevel logistic regression models estimated odds ratios of late-stage cancer diagnosis associated with increases in primary care physician density by insurance type. Analyses were conducted in 2014. RESULTS Decreases in late-stage diagnosis of cancers of the breast, prostate, melanoma of the skin, oral cavity and pharynx, or lung/bronchus associated with increases in primary care physician density were strongest among those with private insurance, whereas those with Medicare (prostate, oral cavity and pharynx, lung/bronchus), Medicaid (lung/bronchus), uninsured (prostate), and other/unknown (prostate, oral cavity and pharynx, lung/bronchus) did not benefit as greatly, or experienced significant increases in late-stage cancer diagnosis (other/unknown [female breast], Medicaid [melanoma of the skin], and uninsured [colon/rectum]). CONCLUSIONS As primary care physician density increases, those with private insurance consistently benefit the most in terms of late-stage cancer diagnosis, whereas those with several other insurance types experience flatter decreases or significantly higher odds of late-stage cancer diagnosis.