Background: Acute fibrinous and organizing pneumonia (AFOP) is unique pathological entity with intra alveolar fibrin in the form of "fibrin balls" and organizing pneumonia.It was divided into rare idiopathic interstitial pneumonia (IIP) according to the classification notified by ATS/ERS in 2013.As a rare pathological entity, it is still not well known and recognized by clinicians.We reviewed the clinical features associated with 20 patients with AFOP in patients diagnosed in a teaching hospital.Methods: The medical records of biopsy-proven 20 patients with AFOP were retrospectively reviewed.