We describe a rare case of pulmonary mucinous cystadenoma (PMCA) detected 18F-FDG PET/CT and mimicking a malignancy. A 60-year-old female patient underwent 18F-FDG PET/CT for metabolic characterization of a left pulmonary nodule which showed increased 18F-FDG uptake (SUVmax = 3.7). Based on this PET/CT finding, the patient underwent a cuneiform resection of the left pulmonary nodule. Histology demonstrated the presence of a PMCA. In our case, 18F-FDG PET/CT has been useful in detecting this rare pulmonary tumor.