A 47-year-old male had symptoms of coughing and with fever and was admitted to our hospital where tests revealed he had anemia and thrombocytopenia. Following the results obtained from a bone marrow aspiration, he was diagnosed as having acute myeloid leukemia (AML). A chest radiograph and a CT scan demonstrated nodular shadows and pleural exudate in both lungs. We suspected atypical pneumonia, or fungal pneumonia, and he was subsequently given antibiotics and antifungal agents, which were, however, ineffective. On the third day after admission, he was put on mechanical ventilation, and a bronchoalveolar lavage examination revealed no germs. His respiration, however, progressively worsened and he died on the twelfth day after admission. Although the autopsy findings revealed no infectious lesions in his lungs, a PAS-positive intra-alveolar eosinophilic material, which was positive for surfactant apoprotein A staining, was present. As a result of the autopsy findings, a diagnosis of secondary pulmonary alveolar proteinosis (PAP) associated with AML was made. Among the reported cases of PAP in hematological malignancy, there has not been one case detected at the time AML was diagnosed. If there is evidence of an unknown cause of lung infiltration when AML is diagnosed, attention should be paid to the possibility of the presence of PAP.