Objective To describe and analyze the misdiagnosis and mistreatment status of pulmonary alveolar proteinosis (PAP), especially cases with combination of severe infection. Method The misdiagnosis and mistreatment of 84 PAP patients and 6 cases with combination of severe infection before admitting to PUMCH was analyzed retrospectively. Results 66.7%(56/84) had experienced misdiagnosis before admission. 32.1% (27/84) were misdiagnosed with idiopathic interstitial pneumonia (IIP) and 14.3% (12/84) with pulmonary tuberculosis. 88.1%(74/84) had received anti-infection treatment, 33.3%(28/84) received eortieosteroids, and 19.0%(16/84) received anti-tuberculosis treatment. The percentage of the pa-tients who had taken the bronchoscopic examination outside the PUMCH was 53.6%(45/84). The PAP pa-tients diagnosis was established through bronchoscopic examination (including BAL and TBLB) in 86.9% (73/84) patients. There were 6 patients who had severe infection when PAP established. All of these 6 cases had been misdiagnosed with IIP and received corticosteroids treatment, 2 of whom died. Conclusions The misdiagnosis and mistreatment happens commonly in PAP patients. The misuse of corticosteroids makes some PAP cases get the severe infection. The image feature and the examination of bronchoscopy, BAL and TBLB are the key point in avoiding misdiagnosis. The administration of corticosteroids in uncertain patients should be avoided.