An incidentally found solid solitary pulmonary nodule (SPN) was studied using FDG PET/CT. The SPN (at that time 11mm) showed only minimal FDG uptake, with a maximum standardized uptake value of 1.7 (max SUV). This suggested a benign lesion. When followup CT was performed six months later, the SPN had grown to 12mm. The patient was re-examined by FDG PET/CT five months later to exclude malignancy. The SPN was now FDG avid, and its size was 14mm. The max SUV was 12.7, consistent with a malignant disease. The patient underwent surgery, and histological examination demonstrated a solid adenocarcinoma (gradus III). The increase in glucose metabolism can be attributed to a change in the histopathologic subtype or molecular features of the SPN. The importance of a followup of nonmetabolically active SPNs is emphasized, primarily by CT (due to its convenience and low cost).