ObjectiveTo improve clinicians' knowledge of hypersensitivity pneumonitis (HP). MethodsWe retrospectively analyzed the clinical data of 24 HP patients who were diagnosed in the Affiliated Drum Tower Hospital of Nanjing University Medical School during February 2005 to February 2013. The clinical,radiological and pathological features of those patients were summarized. ResultsAmong those 24 patients,15 were male and 9 were female,with mean age of (48±13) years. All patients had a history of environmental exposure. Two patients showed acute clinical manifestations,and there were 17 subacute and 5 chronic cases. The main clinical manifestations were dyspnea,cough,sputum,fever and weight loss with hypoxemia via blood gas analysis. Restrictive ventilatory impairment was the most frequent functional pattern,and the carbon monoxide diffusing capacity was decreased. Pulmonary function test showed restrictive ventilatory defect and gas interchange disturbance. The features of chest HRCT included diffuse ground-glass attenuation and/or patchy consolidation,centrilobular micronodules,mosaic sign,reticular and/or honeycombing lesions. Bronchoalveolar lavage fluid (BALF) demonstrated an increase of total cell counts with predominant lymphocytosis. The transbronchoscopic lung biopsy (TBLB) pathological examination revealed lymphocytic alveolitis,noncaseating granuloma,and interstial pneumonia. All patients were treated by corticosteroid and avoided antigen exposure and showed significant clinical and radiological improvement. ConclusionThe diagnosis of HP is difficult. In most cases (acute and subacute HP),a diagnosis can be made by combination history of exposure,chest HRCT manifestations,cell classification of BALF and pathological examination of TBLB. For atypical cases (chronic HP),a surgery lung biopsy is needed for multi-disciplinary diagnosis including pathologist,radiologist and pulmonologists.