Bronchogenic carcinomas are rare in childhood. Furthermore, mucinous (so-called colloid) adenocarcinoma, an unusual variant of pulmonary adenocarcinoma, is extremely rare in the first decade of life. To the best of our knowledge, we report the first case with primary pulmonary mucinous adenocarcinoma at the age of 15. Another interesting aspect of this tumor was its metastasis to thyroid, because metastasis of primary bronchogenic carcinomas to thyroid is uncommon. One can face up with difficulties in the establishment of the definite diagnosis due to its complex and often indistinguishable histopathologic pattern. In this paper we report a patient with pulmonary solid mass and thyroid nodule, initially diagnosed as metastatic thyroid carcinoma in whom postoperative resective surgery confirmed primary pulmonary mucinous adenocarcinoma with synchronous metastasis to thyroid.