A 59-year-old man was admitted to our hospital with high fever, non-productive cough, and dyspnea on exertion. Blood tests showed pancytopenia and elevated levels of lactate dehydrogenase and soluble interleukin-2 receptor, suggesting a diagnosis of intravascular lymphoma. Despite lower PaO₂ and low pulmonary diffusing capacity for carbon monoxide, chest computed tomography (CT) scans did not show any abnormalities. Both bone marrow biopsy and random skin biopsy revealed negative results. (¹⁸F)-fluorodeoxyglucose (FDG)-positron emission tomography (PET) CT showed intense FDG uptake in both lower lungs. Transbronchial lung biopsy confirmed the diagnosis of intravascular large B cell lymphoma. In addition, lymphoma cells were found in specimens from the second random skin biopsy. We discuss ways to obtain histopathological confirmation of intravascular lymphoma of the lung.