We report seven cases of metastatic mature teratoma in the lung from testicular teratocarcinoma and embryonal carcinoma. The patients were between 19 and 58 years of age when orchiectomy was performed. The primary tumors each contained a prominent component of embryonal carcinoma as well as mature and immature teratoma in six patients and only embryonal carcinoma in one. In three patients metastatic pulmonary nodules were detected at the time of orchiectomy, and in three others pulmonary metastases occurred 4 and 8 months after orchiectomy. In one patient the interval was 1.5 years; however, chest roentgenography was not performed during that period. All the patients received chemotherapy or radiation therapy prior to removal of the pulmonary metastases. Thoracotomy was performed between 4 months and 9 years after detection of pulmonary metastases on chest roentgenograms. In one patient the procedure consisted of a lobectomy and in another a pneumonectomy. In the remaining five cases excision of the nodules was performed. The pulmonary metastases resected were grossly solitary lesions in five patients and multifocal in two. Microscopically, each tumor consisted entirely of mature teratoma. Cuboidal and mucin-secreting glandular epithelium predominated in the cystic areas; fibroconnective tissue was the predominant feature of the solid areas. In four patients the course has been indolent with no manifestations of the disease after at least 1 year; in two patients no follow-up was obtained; and one patient died, apparently of a septic process. We present a discussion of this interesting and unusual event.