It is difficult to distinguish multiple primary lung cancers from pulmonary metastasis. We experienced a case of surgically resected lung tumors that showed multiple ground-glass opacities on thoracic computed tomographic scan. There were eight nonsolid and two part-solid ground-glass opacities in the bilateral lungs. Surgical resection was performed because all tumors had a ground-glass opacity appearance on computed tomographic scan, which is compatible with a finding of primary lung adenocarcinoma. The postoperative pathologic diagnoses were two cases of invasive adenocarcinoma, six cases of bronchioloalveolar carcinoma, and eight cases of atypical adenomatous hyperplasia. The patient remains alive without any evidence of recurrence 40 months after surgery. A ground-glass opacity appearance on computed tomographic scan could be interpreted as supportive evidence for multiple primary lung adenocarcinoma rather than pulmonary metastases.