Objective We aimed to evaluate the predictive value of delayed 18 F-FDG PET/CT for identifying malignancies involved in the nipple-areolar complex (NAC) in comparison with clinical symptoms and breast MRI. Methods We enrolled 90 patients who underwent preoperative delayed 18 F-FDG PET/CT and MRI between October 2015 and May 2017. We calculated the NAC-Standardized uptake value ratio (SUVR) using the following formula: maximum SUV (SUV max ) of the NAC in the malignant breast /SUV max of the NAC in the contralateral normal breast on early (NAC-SUVR early ) and delayed (NAC-SUVR delay ) phase images. MRI was used to measure the distance between the tumor and NAC and to analyze NAC enhancement patterns. Univariate and multivariate analyses were performed to identify significant predictive factors for NAC involvement. Results Seventeen patients were confirmed to have pathologic NAC involvement. NAC symptoms (p = 0.009), tumor multiplicity (p = 0.006), NAC-SUVR delay (> 1.23, p = 0.007), and MRI-based tumor-to-NAC distance ( 22.0 mm, p = 0.003) were independent predictive factors for NAC involvement. Ten of 76 patients with no clinical NAC symptoms had NAC malignancy. Tumor multiplicity (p = 0.009), tumor-to-NAC distance ( 20.0 mm, p = 0.014)), and NAC-SUVR delay (> 1.23, p = 0.018) had independent predictive value for NAC involvement. Conclusions Delayed 18 F-FDG PET/CT is a useful modality for predicting NAC involvement in breast cancer patients whether or not NAC symptoms are present.