Two women, 56 years old (patient 1) and 59 years old (patient 2), commonly had a one month history of fever, weight loss, and upper respiratory symptoms. They did not show skin lesions and hepatosplenomegaly. Chest computed tomography (CT) scans also commonly showed ground-glass opacities and consolidations in both lungs (Fig. 1). In the bone marrow study, secondary hemophagocytosis (patient 1) and lymphoma involvement (patient 2) were observed, respectively. A positron emission tomography (PET) scan with 2 patients revealed diffuse increased glucose uptake in both of the lungs. These findings of CT scan and PET scan considered atypical bacterial or viral pneumonia, and acute hypersensitivity pneumonitis as possible diagnosis. An open lung biopsy for a confirmative diagnosis showed that CD20, CD79a, bcl-2, and MUM-1 were positive in the intravascular atypical cells (Fig. 1). Patient 1 was given best supportive care because of poor general condition due to delayed diagnosis. It was much delayed (2 months [patient 1], 1 month [patient 2], respectively) to diagnose finally from the initial hospital visit. On several reports, the prognosis of IVL is very poor, early introduction of systemic chemotherapy may be important to improve prognosis (46). The previous reports recommended an anthracycline-based chemotherapy regimen including CHOP. Rituximab is added in cases of B-cell lineage (236). Therefore we decided to use intensive chemotherapy for patient 2, who was given 3 cycles of R-hyper CVAD regimen. After 2 cycles of R-hyper CVAD, partial remission was observed. However, disease rapidly progressed and the patients eventually expired at three (patient 1) and four months (patient 2) after initial presentation, respectively. For early diagnosis of IVL with lung involvement, the early suspect based on symptoms, chest CT scan and PET scan are important because of no specific findings for IVL of lung involvement, and early aggressive diagnostic procedures (such as trans-bronchial biopsy, open lung biopsy) are required. Because the prognosis of IVL is poor, the more intensive treatment including front-line autologous transplantation should be explored. Here, we reported two cases of intravascular large B-cell lymphoma involving the lungs with their images and histopathology findings.