Lung adenocarcinoma with humeral metastasis as the initial presentation is rare. We reported FDG PET/CT findings of solitary humeral metastasis from adenocarcinoma of the lung in a 57-year-old man with the right upper arm pain as the initial presentation. MRI showed bone destruction of the right humerus with a soft tissue mass, suggesting the possibility of malignancy. FDG PET/CT showed that the right humeral mass had strong activity, and there were additional FDG lesions in the right armpit, left apical lung, and left adrenal gland, which was later confirmed as humeral metastasis from lung adenocarcinoma by pathological examination.