The National Comprehensive Cancer Network (NCCN) guidelines recommend assessment with positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) in staging of breast cancer, starting from the stage IIIA. Previously, PET/CT contributed to the accurate staging from the stage IIB. Our aim is to evaluate the contribution of 18F-FDG PET/CT in staging of breast cancer patients. A total of 234 patients were retrospectively evaluated. PET/CT was performed preoperatively in 114/234 and postoperatively in 120/234 patients. Initial staging was performed based on histopathological results in 125/234 and clinical results in 109/234 patients, according to the American Joint Committee on Cancer (AJCC) classification. All patients had a normal abdominal ultrasound and chest x-ray. Following PET/CT imaging, modification in the staging was performed in patients with the metastatic findings. In 42/234 (17.9%) patients hypermetabolic extra-axillary regional lymph nodes and in 65/234 patients (27.7%) distant metastatic involvement were detected with PET/CT. Modification in the staging was applied in 82/234 (35%) patients. Patient management was changed in 69/234 (29.4%) cases. The percentage of patients with upstaging, according to each stage, was as follows: IIA: 18.6%, IIB: 30%, IIIA: 46.3%, IIIB: 68.8%, and IIIC: 20.8%. In 43/43 patients, 99mTc-methylene diphosphonate (MDP) bone scan did not show additional bone metastasis. In 5/32 patients, metastatic involvement was detected with sentinel lymph node biopsy (SLNB), but preoperative PET/CT scan did not reveal hypermetabolic lymph nodes. Although our study was limited by the referral bias and lack of homogeneity in the referral group, PET/CT still significantly contributed to the accurate staging and management of our breast cancer patients, starting from the stage IIA.