[en] Purpose: To investigate the potential effect of using ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) in the initial assessment of patients with clinical Stage II or III breast cancer. Methods and Materials: During 14 consecutive months, 39 patients (40 tumors) who presented with Stage II or III breast cancer on the basis of a routine extension assessment were prospectively included in this study. PET/CT was performed in addition to the initial assessment. Results: In 3 cases, PET/CT showed extra-axillary lymph node involvement that had not been demonstrated with conventional techniques. Two of these patients had hypermetabolic lymph nodes in the subpectoral and infraclavicular regions, and the third had a hypermetabolic internal mammary node. PET/CT showed distant uptake in 4 women. Of these 4 women, 1 had pleural involvement and 3 had bone metastasis. Overall, of the 39 women, the PET/CT results modified the initial stage in 7 (18%). The modified staging altered the treatment plan for 5 patients (13%). It led to radiotherapy in 4 patients (bone metastasis, pleural lesion, subpectoral lymph nodes, and internal mammary nodes) and excision of, and radiotherapy to, the infraclavicular lymph nodes in 1 patient. Conclusions: PET/CT can provide information on extra-axillary lymph node involvement and can uncover occult distant metastases in a significant percentage of patients. Therefore, initial PET/CT could enable better treatment planning for patients with Stage II and III breast cancer