The classification of thyroid nodules in children is often difficult, especially in pretreated patients with metastatic disease. In osteosarcoma patients, 99mTc-MDP SPECT/CT is used for primary and follow-up staging. Bone and soft tissue metastases can be revealed because of 99mTc-MDP imaging of osteoid-producing metastases. We present 99mTc-MDP SPECT-CT, CT, and ultrasound images of a highly suspicious calcified thyroid lesion in a 17-year-old boy with osteosarcoma. High uptake in 99mTc-MDP SPECT-CT provides diagnosis of thyroid metastasis of osteosarcoma, which was proven by histopathology.