BACKGROUND Intravascular large B-cell lymphoma (IVLBCL) is a rare extranodal large B-cell lymphoma characterized by the selective growth of lymphoma cells within vasculature. This presents a diagnostic challenge due to non-specific symptoms and lack of tumor formation. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) provides useful information in diagnosing FDG-avid lymphoma, but is not specific to IVLBCL. Contrast-enhanced ultrasonography (CEUS) is useful in evaluating focal liver lesions; however, its efficacy in diagnosing IVLBCL involving the liver remains unknown. CASE REPORT We report the case of an 83-year-old woman presenting with fever, pancytopenia, liver dysfunction, and elevated LD and soluble interleukin-2 receptor levels. PET-CT showed multiple uptake lesions in the liver. We performed CEUS with Sonazoid® to evaluate the mass-like lesions; however, no nodular lesions were observed in B mode images. Systemic enhancement was seen in the early phase but no defect was observed in the post-vascular phase. The latter finding suggested preserved Kupffer cells function, excluding tumor-forming lymphoma and liver metastases. Suspecting IVLBCL, we performed a bone marrow examination, which showed sinusoidal infiltration of large neoplastic cells positive for CD20. The patient's condition deteriorated rapidly and she died 2 days after the examination. Autopsy revealed diffuse infiltration of lymphoma cells into liver sinusoids with preserved Kupffer cells, leading to the diagnosis of IVLBCL. CONCLUSIONS Our case shows that CEUS can distinguish IVLBCL from mass-forming lymphoma based on the absence of a defect in the post-vascular phase in a patient with clinically and radiographically suspected lymphoma involving the liver. This can assist clinicians to select appropriate lesions for biopsy.