The thyroid gland is a very rare location of metastasis and the metastatic involvement of the thyroid is mostly asymptomatic. The authors report one of the first cases of pulmonary adenocarcinoma associated with painful metastatic involvement of the thyroid gland. Temporary hyperthyroidism was noted, followed, two months later, by clinically and biologically proven hypothyroidism with positive antithyroglobulin antibodies. The suspect goiter was detected by diffuse hyperfixation on 18-FDG PET Scan and the ultrasonography revealed two hypoechogenic nodules. The fine needle biopsy confirmed the metastatic origin of these nodules. The evolution after five cycles of chemotherapy by cisplatine and docetaxel was marked by a complete regression of the thyroid metastasis and an improvement in the thyroid function.