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 fluorodeox-yglucose (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.