['To estimate the frequency of ambulatory care-sensitive hospitalizations (ACSHs) and to compare the risk of ACSH in breast cancer survivors living in high-poverty with that of those in low-poverty areas.', 'Prospective, multilevel study.', 'National, population-based 1991 to 1999 National Cancer Institute Surveillance, Epidemiology, and End Results Program data linked with Medicare claims data throughout the United States.', 'Breast cancer survivors aged 66 and older.', 'ACSH was classified according to diagnosis at hospitalization. The percentage of the population living below the U.S. federal poverty line was calculated at the census-tract level. Potential confounders included demographic characteristics, comorbidity, tumor and treatment factors, and availability of medical care.', 'Of 47,643 women, 13.3% had at least one ACSH. Women who lived in high-poverty census tracts (>or=30% poverty rate) were 1.5 times (95% confidence interval (CI)=1.34-1.72) as likely to have at least one ACSH after diagnosis as women who lived in low-poverty census tracts (<10% poverty rate). After adjusting for most confounders, results remained unchanged. After adjustment for comorbidity, the hazard ratio (HR) was reduced to 1.34 (95% CI=1.18-1.52), but adjusting for all variables did not further reduce the risk of ACSH associated with poverty rate beyond adjustment for comorbidity (HR=1.37, 95% CI=1.19-1.58).'] Is area-level poverty associated with greater risk of ambulatory-care-sensitive hospitalizations in older breast cancer survivors?