The breast is an extremely rare site for metastases from thyroid malignancies, with very few reports in the literature, the majority of them featured in the histopathology and cytopathology literature. Overall, breast metastases from extramammary primary malignancies represent around 2% of breast tumors. This report describes a case of medullary carcinoma of the thyroid (MCT) metastatic to the left breast that was detected by FDG-PET imaging. A 32-year-old woman, a diagnosed patient with MCT, presented with rising calcitonin for which she was referred for metastatic survey. A whole body FDG-PET revealed a solitary focus of intense FDG uptake in the upper outer quadrant of the left breast. This was subsequently biopsied and the histopathology turned out to be metastasis from the MCT. Breast metastasis is unusual in the natural history of medullary carcinoma of the thyroid and hence presented here as an interesting unusual variant. Detection of atypical metastases can render valuable insight into hitherto unexplored disease progression mechanisms in oncology practice. FDG-PET with its distinct advantage to do a whole body survey in a single examination can play a pivotal role in this respect.