A 44-year-old man with total thyroidectomy for papillary thyroid carcinoma (PTC) performed at the age of 38 years was referred for mediastinal metastases demonstrated on chest radiograph and high serum thyroglobulin (Tg 328 ng/ml). Computed tomography revealed mediastinal lymph node enlargement with left bronchial compression and reduction of bronchial diameter, as well as two metastases in the left lung. Bronchoscopic biopsy findings showed a poorly-differentiated PTC, while a whole body scan after 131-Iodine therapy demonstrated uptake in the right subclavicular region. External beam radiotherapy and chemotherapy yielded no benefit; the neoplasm was aggressive, diffuse and experienced fast growth, leading to the formation of metastases also at unusual sites, such as the skin and thigh muscle. The patient died from a brain metastasis. We report a rare case of PTC metastasis with a poorly-differentiated component in a young patient. Rapid and diffuse metastases also to unusual sites led to death eight years after the initial diagnosis and treatment.