A 72-year-old man suffered from paraparesis with a sensory impairment and bladder and rectal disturbances. Magnetic resonance imaging T2-weighted images depicted a high-intensity lesion in the spinal cord that was consistent with myelitis. A blood examination revealed severe thrombocytopenia and liver dysfunction. No malignant cells were detected by peripheral smears or bone marrow biopsy. Systemic computed tomography detected hepatosplenomegaly and ascites but no lymphadenopathies. Transjugular liver biopsy (TJLB) safely confirmed a diagnosis of intravascular large B-cell lymphoma (IVLBCL), and the patient achieved a complete response following treatment with an appropriate chemotherapy. TJLB is therefore a timely and accurate diagnostic approach for IVLBCL, especially when a bleeding tendency and ascites are noted.