Inflammatory breast cancer (IBC) is the most aggressive form of locally advanced breast cancer. It can be diagnosed based on a clinical or pathologic basis. We evaluated the usefulness of (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) scans for diagnosing and staging IBC. We retrospectively reviewed the medical records of seven consecutive patients with IBC who underwent FDG-PET scanning for the initial staging. Four patients had follow-up PET scans after chemotherapy. All seven patients presented with diffuse breast enlargement, redness, and peau d'orange for 1 to 5 months' duration. In addition, four patients had a palpable breast mass, and three had axillary lymph node enlargement. Mammography showed diffuse, increased parenchymal density and skin thickening in 85% and parenchymal distortion in 43%. There was no evidence of distant metastasis on computed tomography of the chest or abdomen. Pathologic examination of breast biopsy specimens showed infiltrating ductal carcinoma in six patients, and one had lobular carcinoma. All patients had prechemotherapy whole-body PET scans that showed diffuse FDG uptake in the breast with superimposed intense foci in the primary tumor. Furthermore, there was skin enhancement in 100%, axillary lymph node in 85%, and skeletal metastases in 14% of the patients, confirmed by bone scintigraphy. Postchemotherapy FDG-PET scans performed in four patients showed response in the primary tumor, axillary lymph nodes, and skeletal metastases. The FDG-PET scan is thus useful for displaying the pattern of FDG breast uptake that reflects the extent of the pathologic involvement in IBC (i.e., diffuse breast involvement and dermal lymphatic spread). It can also detect the presence of lymph node and skeletal metastases, demarcating the extent of the disease locally as well as distally.