Numerous studies have convincingly shown that women with low bone mineral density have lower risk of breast cancer. As many risk factors for breast cancer are also prognostic factors, we hypothesized that women with breast cancer and low bone mineral density will have lower breast cancer recurrence rates than women with normal bone densities. A prospectively collected data base of breast cancer patients was used to identify postmenopausal Caucasian women. Their records were reviewed and 309 patients with complete follow-up and bone density tests within 1 year of their surgery were identified. The outcome of patients with low bone density (t > −1.0) was compared to the outcome for patients with normal bone density (t < −1.1). Among the 193 patients with invasive breast cancers and low bone density, distant disease-free survival at 5 years was 96% compared to 84% for 114 patients with invasive breast cancers and normal bone density (p = 0.0239). Local disease-free survival was 94% for low bone density patients compared to 86% for patients with normal bone densities (p = 0.0794). Bone mineral density is a significant prognostic factor for postmenopausal Caucasian women with breast cancer. Low bone mineral density is associated with a lower local and distant rate of recurrence.