Purpose To determine the prognostic implications of pretreatment F-18 FDG PET/CT in patients with invasive ductal breast cancer (IDC), we evaluated the relationship between FDG uptake of the primary tumor and known prognostic parameters of breast cancer. Prognostic significance of tumoral FDG uptake for the prediction of progression-free survival (PFS) was also assessed. Materials and Methods Fifty-five female patients with IDC who underwent pretreatment F-18 FDG PET/CT were enrolled. The maximum standardized uptake value of the primary tumor (pSUVmax) was compared with clinicopathological parameters including tumor size, grade, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor2 (HER2), axillary lymph node (LN) metastasis, and stage. The prognostic value of pSUVmax for PFS was assessed using the Kaplan-Meier method. Results A high pSUVmax was significantly related to a higher stage of tumor size (P<0.05), grade (P<0.001), and stage (P<0.001). pSUVmax was significantly higher in ER-negative tumors (P<0.001), PR-negative tumors (P<0.001), and positive LN metastasis (P<0.01), but not different according to HER2 status. pSUVmax was significantly higher in patients with progression compared to patients who were disease-free ($10.6{pm}5.1$ vs. $4.7{pm}3.5$, P<0.001). A receiver-operating characteristic curve demonstrated a pSUVmax of 6.6 to be the optimal cutoff for predicting PFS (sensitivity; 86.7%, specificity; 82.5%). The patients with a high pSUVmax (more than 6.6) had significantly shorter PFS compared to patients with a low pSUVmax (P<0.0001). Conclusions pSUVmax on pretreatment F-18 FDG PET/CT could be used as a good surrogate marker for the prediction of progression in patients with IDC.