Ground-glass opacity is a frequent but nonspecific finding seen on high-resolution CT scans of lung parenchyma. Histologically, this appearance is observed when thickening of the alveolar wall and septal interstitium is minimal or the alveolar lumen is partially filled with fluid, macrophage, neutrophils, or amorphous material. It has been shown that ground-glass opacity may be caused not only by an active inflammatory process but also by fibrotic processes. When a focal area of ground-glass opacity persists or increases in size, the possibility of neoplasm-bronchioloalveolar carcinoma or adenoma, or lymphoma, for example- should be considered. Diffuse nonsegmental ground-glass opacity in both lung fields was incidentally found on follow up abdominal CT in a stomach cancer patient and signet-ring cell-type metastatic lung cancer was confirmed by transbronchial lung biopsy. We report a case of diffuse ground-glass opacity seen in metastatic lung cancer from adenocarcinoma of the stomach.