To characterize the clinical features of patients with idiopathic pulmonary fibrosis (IPF) having organizing pneumonia (OP), we retrospectively reviewed the clinical charts, chest X-rays, CT scans, and transbronchial lung biopsy (TBLB) specimens of patients with IPF. Patients with IPF and OP had a subacute onset of symptoms (within 2 months) (87.5%), leukocytosis (> 10,000/mm3) (62.5%), and a strong C-reactive protein (CRP) reaction (> 3+) (75%). Some of these features were distinctly different from those of IPF patients without OP (subacute onset of symptoms 0%, leukocytosis 0%, strong CRP reaction 16.7%). In the patients with IPF with OP, A-aDo2 and semiquantitative scores of chest X-ray abnormalities improved significantly after prednisolone treatment. Those abnormalities improved only slightly in the patients with IPF without OP. Diffusing capacity remained decreased and abnormal interstitial infiltration persisted, even after prednisolone treatment in the patients with IPF with or without OP. Clinical features of IPF patients with OP differed from those of patients with IPF without OP. IPF patients with OP showed good clinical response to corticosteroid therapy. These findings warrant further study of the presence of OP in TBLB specimens in predicting corticosteroid responsiveness and prognosis of patients with IPF.