The brain and spinal cord from 14 patients with primary central nervous system lymphomas (PCNSL) were systematically examined to determine the distribution and frequency of spinal cord lesions. Spinal cord involvement was observed in four cases (cases 1-4). In cases 1 and 2, tumor cells were spread widely in the brain and extended downward to C4 and Th8 in the spinal parenchyma and to C2 and Th2 in the subarachnoid space (SAS), respectively. In case 3, tumors were found in the cerebrum but not in the cerebellum or brainstem. In the spinal cord there was massive subarachnoid involvement from C2 to L4 and localized parenchymal invasion from Th8 to L4. In case 4, tumors were found in the parenchyma from brainstem to Th2 and in the SAS all around the cord. Diffuse subarachnoid proliferation with parenchymal invasion via the Virchow-Robin space was found in the spinal cord. The route of tumor spread in cases 1 and 2 was considered to be intra-parenchymal invasion from the medulla oblongata to the spinal cord because the cord lesions had continuity with the brain lesions. In contrast, the cord lesions in cases 3 and 4 were considered to be spread via the CSF because the lesions had no continuity with the brain lesions in case 3, and spinal SAS involvement was more extensive than the parenchymal lesions in both cases. These findings suggest that spinal cord involvement is not a rare event in PCNSL and that there are two routes of spread: direct invasion from the medulla oblongata and dissemination via the CSF.