BACKGROUND: The purpose of this study was to identify correlates of HER2 status for patients with bilateral breast cancer. METHODS: Data were collected prospectively in our institutional review board approved patient registry for all patients with asynchronous (ABBC) and synchronous (SBBC) bilateral infiltrating breast cancer whose HER2 assays were performed at our laboratory using FISH. Data were analyzed using the Wilcoxon rank sum and Chi-square test. RESULTS: Data were available for 98 tumors in 49 patients. Patients diagnosed with SBBC were more likely to be white (P = 0.023); to have bilateral HER2 non-amplified tumors (P = 0.022) and to be older at diagnosis (P = 0.025) compared to those with ABBC. Patients with one HER2 amplified tumor were likely to have at least one tumor be hormone receptor negative and to have ABBC. CONCLUSIONS: Only 16% of patients in this study had one tumor that was HER2 amplified; no patient had bilateral HER2 amplified tumors.