PURPOSE: PET developed on the basis of biochemical characteristics of malignant tissues where the increase in glucose metabolism. Therefore, early and accurate detection of primary or metastatic lesion can be expected. This study is to compare PET and other traditional methods in detection of primary breast carcinoma and metastatic lesion, and to find the advantage of PET. MATERIALS AND METHODS: We compared and analysed the results of PET, US, mammogr aphy, bone scan, CT and biopsy reports of the 46 patients who were examined in our hospital from September 1, 19094 to July 31, 1995. PET Trace 200 cyclotron and PET Advanced Scenner were used for FDG synthesis and imaging respectively. RESULTS: 10 of the 12 cases who had preoperative PET were consistent with the results of mammography and ultrasound and 9 of the 10 cases were consistent with the pathologic results. In one case, which did mammography and PET after excis ional biopsy, PET gaves a false positive result. In the detection of axilliary node metastasis, PeT after excisional biopsy, PET gaves a false positive result. In the detection of axilliary node metastasis, PET shows 100% sensitivity and specificity but bone scan shows 100%, 72.2% respectively. CONCLUSION: PET is useful for diagnosis of primary breast cancer and is superior to bone scan in specificity for diagnosis of bone metastasis and in early detection of response to treatment. Because PET cannot exclude false (+) in inflamm atory lesion, continuous investigation is needed for establishment of indication and reduction of false (+), false (-).In spite of high cost, PET may become a new and useful diagnostic tool.