Background: Diabetes has been associated with an increased risk of mortality among patients with many types of cancers. Methods: We performed a case-control study of 109 breast cancer patients to determine the impact of diabetes on disease recurrence and survival. These 109 patients diagnosed with invasive breast cancer during 2007-2011 with diabetes were identified from the institutional Cancer Registry and matched to 109 breast cancer patients without diabetes according to age, race/ethnicity and year of diagnosis. Statistical tests included paired t-tests, McNemar’s tests, and stratified Cox regression. Results: The median ages of those with and without diabetes were 68 years, and 91% in both groups were white (both matched). Patients with and without diabetes were not significantly different in terms of tumor grade, cancer stage, estrogen or progesterone receptor status, HER2 neu status, marital and employment status, smoking use, use of adjuvant chemotherapy, and steroid treatment (all P >.4). Patients with diabetes reported less use of alcohol (50% vs 64%, P=.04), and had greater BMI (79% overweight/obese vs 58%, P= .002). Survival analysis demonstrated no differences in survival from initial breast cancer diagnosis (HR=1.25, 95% CI 0.49-3.17) with median follow-up of 2.2 years (range 0.1-4.9), and no differences in recurrence-free survival (HR=1.00, 95% CI 0.14-7.10) though very few deaths and recurrences were observed. Within the diabetes group, 96 (88%) had type 2 diabetes and 97/106 (92%, 3 unknown) had diabetes pre-existing to cancer diagnosis. Initial diabetes therapy included diet (33, 30%), oral therapy (48, 44%), insulin (21, 19%), or oral+insulin (6, 6%). 7 patients required a change in diabetes therapy within 1 year of cancer diagnosis with 3 patients starting insulin. 32/70 (46%) with available lab data had 1 or more A1C >/=7 within 1 year of cancer diagnosis. Conclusions: In this retrospective, carefully matched case-control study, we developed a comprehensive profile of the patient population with newly diagnosed breast cancer and diabetes. Diabetes did not appear to impact mortality or recurrence-free survival based on descriptive estimates in this small breast cancer cohort.