A 73-year-old man experienced chest tightness and shortness of breath for 9 months. Chest CT revealed a large right upper lobe mass. Pathology from CT-guided biopsy demonstrated poorly differentiated adenocarcinoma of the lung. Whole-body bone scan was acquired to evaluate possible bone metastasis. However, he was injected with 99mTcO4
− erroneously instead of 99mTc-MDP. The images showed a focus of elevated activity of 99mTcO4
− in the known lung lesion.