A 33-year-old woman in the 6th month postpartum and breast-feeding period suffered from acute thoracolumbar pain for 1 month. She presented with slightly decreased serum calcium level. Other laboratory assessments were unremarkable. Considering the worsening symptom and her strong demand to exclude potential malignancy, F-FDG PET/CT was performed. Multiple FDG-avid foci in the thoracic and lumbar vertebra were detected on FDG PET, corresponding to vertebral compression fractures on CT, and diffuse FDG uptake was seen within bilateral breast, and dual-X ray absorptiometry showed markedly decreased bone mineral density, all of which supported the diagnosis of pregnancy and lactation-associated osteoporosis.