Pulmonary mucosa-associated lymphoid tissue-derived (MALT) lymphoma is a rare disease. This disorder is considered to be a model of antigen-driven lymphoma, which is driven either by autoantigens or by chronic inflammatory conditions. Low-grade B-cell MALT lymphoma may develop from a nonneoplastic pulmonary lymphoproliferative disorder, such as lymphocytic interstitial pneumonitis (LIP). A recent estimate predicts that less than 5% of LIP patients acquire malignant, low-grade, B-cell lymphoma. In Korea, there has been no previous report of malignant low-grade, B-cell lymphoma, acquired from LIP. Here, we present the case of a patient with LIP that developed into pulmonary MALT lymphoma, six years after diagnosis.