Purpose: The objective of this study was to evaluate whether uptake on 18F-fluorodeoxyglucose ( 18F-FDG) PET could help differentiate HER2-positive from HER2-negative breast cancer brain metastases. Methods: In this retrospective, cross-sectional study of a cohort of 14 histologically proven breast cancer brain metastases, we analyzed both preoperative 18F-FDG PET/CT and HER2 status of the resected/biopsied brain specimens. The maximum standardized uptake values (SUVmax) of the lesions were normalized to contralateral normal white matter and compared using Mann–Whitney U tests. Results: The study cohort was comprised of 12 women with breast cancer with a mean age of 59 years (range: 43–76 years) with a total of 14 distinct brain metastatic lesions. The SUVmax ratio of HER2-positive breast cancer brain metastases was significantly greater than that of HER2-negative lesions (3.98 vs 1.79, U = 38.00, p = 0.008). Conclusion The SUVmax ratio may help to identify the HER2 status of breast cancer brain metastases, if validated prospectively.