Objective We aimed to evaluate the availability of fluorine-18-fluorodeoxyglucose (18F-FDG) PET/computed tomography (CT) in initial axillary lymph node (ALN) staging in breast cancer. The secondary objective is to evaluate the role of FDG PET/CT as a pretest in sentinel lymph node biopsy vs. axillary lymph node dissection when predicting disease aggressiveness. Methods The study evaluated retrospectively 194 breast cancer patients who underwent preoperative 18F-FDG. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of FDG PET/CT for ALN metastases were confirmed with histopathology as the gold standard. Results The value of the area under curve (AUC), sensitivity and specificity for ALN metastases were determined as 0.847, 78.8% and 92.6%, respectively. The cut-off value of the maximum standardized uptake value (SUVmax) for metastatic ALN detection was calculated as 1.79. PPV, NPV and the accuracy of 18F-FDG PET/CT were 0.933 (93.3%), 0.75 (75%) and 0.837 (83.7%), respectively. The SUVmax value of the primary lesion was significantly correlated with grade, estrogen receptor (ER) status, progesterone receptor (PR) status, SUVmax value of metastatic ALN, Her-2 status and Ki-67 level. Molecular subtypes revealed no statistically significant difference in terms of mean SUVmax value. Conclusion High values of AUC, sensitivity, specificity, NPV and PPV encourage utilization of PET/CT for locoregional staging of nonmetastatic breast carcinoma. The significant correlation between the primary tumor SUVmax value and grade, ER status, PR status and Ki-67 level increases the prognostic predictive value of the preoperative PET/CT.