BACKGROUND: Of the approximately 2.4 million American women with a history of breast cancer, 43% are aged >/= 65 years and are at risk for developing subsequent malignancies. METHODS: Women from 6 geographically diverse sites included 5-year breast cancer survivors (N = 1361) who were diagnosed between 1990 and 1994 at age >/= 65 years with stage I or II disease and a comparison group of women without breast cancer (N = 1361). Women in the comparison group were age-matched and site-matched to breast cancer survivors on the date of breast cancer diagnosis. Follow-up began 5 years after the index date (survivor diagnosis date or comparison enrollment date) until death, disenrollment, or through 15 years after the index date. Data were collected from medical records and electronic sources (cancer registry, administrative, clinical, National Death Index). Analyses included descriptive statistics, crude incidence rates, and Cox proportional hazards regression models for estimating the risk of incident malignancy and were adjusted for death as a competing risk. RESULTS: Survivors and women in the comparison group were similar: >82% were white, 55% had a Charlson Comorbidity Index of 0, and >/= 73% had a body mass index