The value of whole body positron emission tomography using F-18 2-deoxy-2-fluoro-d-glucose in primary work-up and follow-up was prospectively evaluated in 37 patients with primary or metastatic breast cancer. From 20 primary breast masses 15 from 16 malignant and 4 from 4 benign lesions confirmed by biopsy, were detected. In 3 out of 21 patients in correlation to morphologic imaging, respectively biopsy, no metastatic disease was not identified. Generally speaking, whole body positron emission tomography appears to be a suitable diagnostic staging tool in breast cancer.