Purpose The aim of this study was to assess the accuracy of 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT to visualize lymph node metastases before the start of neoadjuvant chemotherapy and to determine how often the visualization is sufficiently prominent to allow monitoring of the axillary response. Methods Thirty-eight patients with invasive breast cancer of >3 cm and/or lymph node metastasis underwent FDG PET/CT before neoadjuvant chemotherapy. The results of the FDG PET/CT were compared with those from ultrasonography with fine-needle aspiration (FNA) cytology or sentinel node biopsy. Patients suitable for response monitoring of the axilla were defined as having either a maximum standardized uptake value (SUV max ) ≥ 2.5 or a tumour to background ratio ≥5 in the most intense lymph node. Results The sensitivity and specificity of FDG PET/CT in detecting axillary involvement were 97 and 100%, respectively. No difference existed between the SUV max of the primary tumour and that from the related most intense lymph node metastasis. Moreover, the mean tumour to background ratio was 90% higher in the lymph nodes compared to the primary tumour ( p  = 0.006). Ninety-three per cent of the patients had sufficient uptake in the lymph nodes to qualify for subsequent response monitoring of the axilla. A considerable distinction in metabolic activity was observed between the different subtypes of breast cancer. The mean SUV max in lymph node metastases of oestrogen receptor (ER)-positive, triple-negative and human epidermal growth factor receptor 2 (HER2)-positive tumours was 6.6, 11.6 and 6.6, respectively. Conclusion The high accuracy in visualizing lymph node metastases and the sufficiently high SUV max and tumour to background ratio at baseline suggest that it is feasible to monitor the axillary response with FDG PET/CT, especially in triple-negative tumours.