Acute exacerbation of interstitial pneumonia is a new terminology with recent debated criteria. Its prognosis is bad and its management remains non consensual. This lack of consensus seems to be due to the lack of knowledge concerning the physiopathologic phenomenon. This lack of knowledge results in few efficient therapeutics. The diagnosis of acute exacerbation is challenging for clinicians and the real place of the pathologic exam remains unknown. Our aim was to assess the different situations faced by the pathologists by emphasizing their real role.