Cryptogenic organizing pneumonia is a rare, distinct disorder that is sufficiently different from the other diseases in the group of idiopathic interstitial pneumonias to be designated as a separate entity. In its most typical presentation, it is characterized by dyspnea and cough, with multiple patchy alveolar opacities on pulmonary imaging. Definite diagnosis is obtained by the finding of buds of granulation tissue in the distal airspaces at lung biopsy. No cause (as infection, drug reaction, or associated disease as connective tissue disease) is found. Corticosteroid treatment is rapidly effective, but relapses are common on reducing or stopping treatment.