Gardner syndrome is characterized by multiple intestinal polyps and extraintestinal lesions. We describe FDG PET/CT findings of the extraintestinal lesions in a patient with Gardner syndrome. FDG PET/CT showed 2 hypermetabolic desmoid tumors in the abdominal wall, sclerotic areas with multifocal activity in the maxilla and mandible, multiple osteomas in the bilateral parietal, left frontal, sphenoid and ethmoid bones, an impacted tooth in the right maxilla, and bone islands in the T2 and T5 vertebral bodies. Extraintestinal involvements in Gardner syndrome can precede intestinal polyposis. Therefore, familiarity with FDG PET/CT findings of extraintestinal manifestations is helpful for early diagnosis.