The value of whole body positron emission tomography using 18F-fluoro-deoxy-glucose (18FDG) in primary work-up and follow-up was evaluated retrospectively in 104 patients with primary or metastatic breast cancer. Compared to other imaging methods, FDG-PET sensitivity was superior to sonography, CT or MRT. Another advantage is the possibility of whole body imaging and the earlier detection of lymph node metastasis due to the recognition of functional metabolic changes compared to structural changes found with conventional imaging methods.