Significant age-related variation in chemotherapy use has been observed among elderly patients with metastatic breast cancer (MBC), which may be partly attributable to geographic access factors such as local area physician practice culture and local health care system capacity. The purpose of the paper was to examine how age may modify the effect of geographic access on chemotherapy use in elderly patients with MBC. This was a retrospective cohort study based on the surveillance, epidemiology, and end results-Medicare-linked database of 1992-2002. Chemotherapy use was defined as at least one chemotherapy-related claim within 6-month post-diagnosis. Geographic access to cancer care was measured by four variables: patient travel time to the nearest oncologist practice, local area per capita number of oncologists, local area per capita number of hospices, and local area chemotherapy rate. Using multivariate logistic regression model, both aggregate models with interaction terms and subgroup analyses were conducted. Among 4,533 elderly with MBC, 30.16 % used chemotherapy. Chemotherapy use decreased with age. Both the aggregate model with interaction terms and the subgroup analysis showed that local area chemotherapy rate was positively associated with chemotherapy use (P = .0004 in the whole group; in the subgroup analyses, P < .0001, P = .0006, P = .0006, P = .18, P = .026, respectively). In addition, subgroup analysis showed that, among patients aged 85+ years old, local area oncologist supply was negatively associated with chemotherapy use (P = .028). The impact of geographic access to cancer care is the greatest among the oldest group, for whom the clinical evidence is the least certain.