Intravascular lymphoma (IVL) is a rare form of non-Hodgkin's lymphoma that is characterized by the preferential growth of malignant lymphocytes within blood vessels. Pulmonary presentation of IVL is uncommon, and only a few cases have been reported in Korea. Here, we report on a 59-year-old woman with relapsed intravascular large B-cell lymphoma in the lungs. She had been treated with 6 cycles of rituximab, cyclophosphamide, adriamycin, vincristine, and prednisolone (R-CHOP) combination chemotherapy for intravascular large B-cell lymphoma in the nasal cavity, and was followed up regularly with no evidence of disease recurrence. About 1 year later, her chest computed tomography showed extensive ground-glass opacity, suggesting interstitial lung disease and, interestingly, diffuse pulmonary fluorodeoxyglucose (FDG) uptake was observed in positron emission tomography (PET). We performed bronchoscopy, bronchoalveolar lavage, and transbronchial lung biopsy. Pathology revealed relapsed intravascular large B-cell lymphoma in the lungs, and she commenced ifosfamide, methotrexate, etoposide, prednisolone (IMVP-16/PD) salvage chemotherapy. After 3 cycles of chemotherapy, PET showed no abnormal FDG uptake. We suggest that a primary or relapsed pulmonary IVL should be considered in the differential diagnosis of unexplained interstitial lung disease and that PET appears be useful in evaluating pulmonary IVL. (Korean J Hematol 2008;43:113-117.)