[en] Radiation interstitial pneumonia (RIP) is a frequent complication in the radiotherapy of intrathoracic malignant tumors, pretreatment of bone marrow transplantation and accident of nuclear radiation. Despite accumulation of abundant information on RIP, its pathogenesis remains unknown up to now. This review sums up three hypotheses of RIP pathogenesis which are inclined to be accepted, these are hypotheses of lung parenchymal cells being the target cells, involvement of lung interstitial infiltration cell and mediation by cytokine