In patients with differentiated thyroid cancer, radioiodine uptake in the area of the lung usually denotes metastasis; however, it could represent an uptake by unrelated pulmonary disease or by the breasts, or external contamination. In this study, 22 foci that simulated lung metastasis on 11 thyroid and whole body scans were proven not to be metastasis by reimaging after cleaning (15 foci), or were strongly suspected to be due to external contamination because of the features of other images (7 foci). All foci were noted only on anterior views of the chest. Of the 22 foci, 19 were focal, two were smeared, and one was lobar. Foci were multiple in 7 scans, unilateral in 10 scans, and were associated with other artifacts in 4 scans. Caution should be used in interpreting apparent pulmonary radioiodine uptake as lung metastasis; reimaging after cleaning the skin and changing garment should be obtained when the uptake is confined to anterior views of the chest and/or when its pattern is atypical.