Mucoepidermoid carcinomas (MECs) represent the most common malignant neoplasms of the salivary glands, but they have also been described in other unusual sites. Primary MECs originating in the thyroid gland are exceedingly rare, accounting for less than 0.5% of thyroid tumors. Owing to their low to medium grade, they are usually associated with an indolent evolution and a good long-term prognosis, generally being managed surgically based on the extent of the disease. However, this does not always apply, as primary thyroid MECs may present as metastatic or locally advanced diseases. While several treatment options have been explored in such cases, no consensus currently exists on their optimal treatment plan, and they should be managed in a multidisciplinary fashion. We report the case of a 67-year-old patient with primary MEC of the thyroid, which behaved aggressively, with extensive pulmonary metastasis, ultimately leading to the rapid clinical deterioration and death of the patient.