BACKGROUND: Here we review primary intrathoracic goiter (P-ITG), a rare but potentially serious congenital entity that is distinct from the much more common secondary intrathoracic goiter. The latter is an extension of cervical thyroid that descends within the mediastinum. In contrast, P-ITGs lack a connection with the cervical thyroid and their blood supply comes from intrathoracic vessels.SUMMARY: P-ITGs can coexist with a normal or goitrous thyroid gland. When they coexist, either or both may be independently affected by neoplastic, infectious, or infiltrative processes. P-ITGs are mainly located in the anterosuperior mediastinum. Location in posterior or middle mediastinum is observed in 15% of cases, making the diagnosis challenging. Although P-ITGs are rare, they are important because they may reach large dimensions with serious consequences. Compression of the trachea is the most common clinical finding, but compression of other mediastinal organs is also observed. Computerized axial tomography (CT) and radionuclide imaging can suggest or make the diagnosis in most cases. The differential diagnosis includes other mediastinal tumors that show high attenuation on unenhanced CT. The treatment of choice is surgical resection of the goiter through a thoracic approach. Thoracic surgery for resection of a small primary mediastinal goiter is considered to be a relatively safe procedure. Long-standing P-ITGs may cause pressure on the trachea, however, resulting in tracheomalacia. This development is serious in its own right and complicates thoracic surgery.CONCLUSIONS: Resection through a thoracic approach is the appropriate treatment for a P-ITG. Surgical intervention is usually indicated without delay upon the establishment of the diagnosis because these goiters exhibit progressive growth. When P-ITGs are small, this approach should prevent the development of tracheomalacia and other serious complications.