A 66-year-old woman was referred for a bone scan to assess back pain on a background of breast cancer, melanoma, and rheumatic heart disease. The scan appearance was suspicious for a localized soft tissue neoplasm. An FDG coincidence positron emission tomography (PET) study demonstrated a large FDG-avid soft tissue abnormality. Staphylococcus aureus was isolated from a subsequent needle biopsy. This case illustrates the use of FDG-PET in infection imaging, as well as demonstrating the potential pitfalls in nuclear oncology. Because FDG is not tumor-specific, accumulation in benign lesions may give rise to false-positive results despite a high pretest probability for malignancy.