To explore the preoperative utility of FDG PET for the diagnosis and prognosis in a retrospective breast cancer case series.In this retrospective study, 104 patients who had undergone a preoperative FDG PET scan for primary breast cancer at the UZ Brussel during the period 2002-2008 were identified. Selection criteria were: histological confirmation, FDG PET performed prior to therapy, and breast surgery integrated into the primary therapy plan. Patterns of increased metabolism were recorded according to the involved locations: breast, ipsilateral axillary region, internal mammary chain, or distant organs. The end-point for the survival analysis using Cox proportional hazards was disease-free survival. The contribution of prognostic factors was evaluated using the Akaike information criterion and the Nagelkerke index.PET positivity was associated with age, gender, tumour location, tumour size >2 cm, lymphovascular invasion, oestrogen and progesterone receptor status. Among 63 patients with a negative axillary PET status, 56 (88.9 %) had three or fewer involved nodes, whereas among 41 patients with a positive axillary PET status, 25 (61.0 %) had more than three positive nodes (P < 0.0001). In the survival analysis of preoperative characteristics, PET axillary node positivity was the foremost statistically significant factor associated with decreased disease-free survival (hazard ratio 2.81, 95% CI 1.17-6.74).Preoperative PET axillary node positivity identified patients with a higher burden of nodal involvement, which might be important for treatment decisions in breast cancer patients.