Positron emission tomography (PET) is an imaging method that employs radionuclide and tomography techniques. PET has high sensitivity for detecting breast cancer, both the primary tumor and axillary node metastasis. From June 1995 to November 1996 a total of 27 patients underwent breast operations based on PET results at Seoul National University Hospital. Whole-body PET images were obtained beginning 60 minutes after injection of 370 MBq (10 mCi) 18F-fluorodeoxyglucose. Regional scans were also obtained with transmission images. We compared the PET results with those from the physical examination and mammography. All cases were histologically confirmed. The diagnostic accuracy of PET was excellent for the primary tumor mass (97%) compared with that of the physical examination (78%) and mammography (67%). For axillary lymph node metastasis, PET had outstanding detection accuracy (96%) compared with the physical examination and mammography (74% and 60%, respectively). Whole-body PET scans made it possible to see all of the metastatic lesions at a glance in cases of metastatic or recurrent breast cancer. There was a probable correlation between the standard uptake value (SUV) and the number of axillary lymph node metastases, but in this study statistical significance was not proved because of the small number of cases. PET also could detect breast cancer in paraffin-augmented breasts. We concluded that PET is a highly sensitive, accurate diagnostic tool for breast cancer and that SUV, after more studies, could be used as an important prognostic factor.