Background SMARCA4-deficient thoracic tumor (SMARCA4-DTT) is a distinct entity of undifferentiated thoracic malignancies newly introduced in 2015. Due to its unique clinical characteristic with aggressive thoracic tumor mostly observed in heavy smoker man with emphysema, with poor prognosis, many physicians are becoming increasingly aware of the disease; however, reports on 2-deoxy-2-[18F] fluoroglucose positron emission tomography/computed tomography ([18F]FDG PET/CT) have been limited; thus, this disease is not yet widely known to nuclear medicine clinicians. As a first step in discussing the usefulness of [18F]FDG PET/CT for this disease, we present a case in which [18F]FDG PET/CT played a clinically important role. Case A 74-year-old heavy smoker man with an anamnesis of severe emphysema characterized by pleural thickening and abnormal enhancement in CT underwent 18F-FDG PET/CT for further examination. [18F]FDG-avid pleural nodules infiltrating into the chest wall were detected and pathologically diagnosed as SMARCA4-DTT with biopsy. Conclusion SMARCA4-deficient thoracic tumor should be considered in a [18F]FDG-avid aggressive thoracic tumor in heavy smoker men with emphysema.