A 90-year-old woman with an abnormal shadow on a chest computed tomography (CT) presented at our hospital. She did not complain of any respiratory symptoms. Chest CT revealed bilateral patchy areas of ground-glass opacities; these areas are referred to as “crazy-paving” patterns. Elevated serum KL-6, SP-D, and CEA levels were observed. Bronchoalveolar lavage and transbronchial lung biopsy were performed, and the lavage fluid had an opaque milky appearance. Histological findings revealed that the alveolar spaces were filled with PAS-positive granular material. The patient also tested positive for the granulocyte-macrophage colony-stimulating factor antibody in the serum (119.6 μg/ml). Based on these findings, the patient was diagnosed with autoimmune pulmonary alveolar proteinosis. The abnormal shadow on the chest CT disappeared after treatment with ambroxol for 6 months.