Autologous fat grafting for cosmetic breast augmentation is becoming increasingly popular. Late complications after intramammary fat injection include fat necrosis, liponecrotic cyst, calcification, and lymphadenopathy. We describe FDG PET/CT findings in a patient with multiple-injection-site fat necrosis after intramammary fat injection. FDG PET/CT showed multifocal activity in the subcutaneous and subglandular regions corresponding to the fat injection sites of the bilateral breasts and multiple FDG-avid lymph nodes of the axillae, mimicking malignancy. Careful correlation with clinical history and familiarity with the imaging findings of the complications after intramammary fat injection are helpful for avoiding misdiagnosis.