Although $^{18}F$-fluorodeoxyglucose ($^{18}F$-FDG) positron emission tomography (PET) is a sensitive modality for detecting a malignant lesion, increased $^{18}F$-FDG uptake is also seen in infected or inflammatory processes. Here, we report the case of a breast cancer patient with concomitant tuberculous axillary lymphadenitis that showed increased $^{18}F$-FDG uptake. A 39-year-old woman underwent preoperative $^{18}F$-FDG PET/computed tomography (CT) as a part of the work-up for right breast cancer. $^{18}F$-FDG PET/CT images showed a malignant lesion in the right breast with moderate $^{18}F$-FDG uptake, and multiple enlarged right axillary lymph nodes with intense $^{18}F$-FDG uptake. Subsequently, the patient underwent right mastectomy and right axillary lymph node dissection. Histopathological examination confirmed breast cancer and tuberculous lymphadenitis, and the patient was treated concomitantly with anti-tuberculous therapy.