During staging workup for lung cancer of a 74-year-old man, 2 more incidental tumors were found on [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT). The 3 sites with cancer in this patient involved organs in which field cancerization has often been described, suggesting that triple primary tumors were more probable than metastasis. After treating them separately, complete response was achieved and sustained for > 2 years. The use of FDG-PET/CT seems necessary to evaluate patients with cancer, especially when there is a reasonable chance for cure. Incidentally identified lesions on FDG-PET/CT should be thoroughly explored to rule out the presence of hidden malignancy and the possibility of synchronous multiple primary tumors.