A 72-year-old female with malignant lymphoma, receiving oral cyclophosphamide (CPA) and prednisone, developed severe pulmonary insufficiency 56 days after the start of CPA (total dosages 8.5 g). A chest roentgenogram showed a diffuse interstitial shadow throughout both lungs, and CT scan revealed increased density, most prominent in the central zones, and a thickening of bronchovascular bundles. She was diagnosed from the clinical course and the postmortem examination as having cyclophosphamide-induced interstitial pneumonia. Interstitial pneumonia as a side-effect of cyclophosphamide is very rare in Japan. The clinical and pathological findings in this case and a review of the literature on 38 other cases world-wide are reported.