In stage III breast carcinoma, metastasized disease needs to be determined. In the past, conventional imaging by liver ultrasound, chest X-ray and bone scintigraphy was the work-up of choice. Recently, FDG-PET/CT was found to have additional value, but clinicians are hesitant to introduce this technique. We present three patients in whom FDG-PET/CT was applied. A 61-year-old woman with stage III breast carcinoma after conventional work-up was upstaged to stage IV breast carcinoma by FDG-PET/CT, upon which her treatment was changed. A 55-year-old woman suspected of stage IV breast carcinoma after conventional imaging was downstaged to stage III after FDG-PET/CT. Her treatment was changed as well. In a 78-year-old woman with recurrent breast carcinoma, the diagnostic certainty of stage III breast carcinoma was increased by FDG-PET/CT. We conclude that FDG-PET/CT is valuable for adequately diagnosing metastases in patients with stage III breast carcinoma and can replace conventional imaging.