An autopsy case of primary intracranial T-cell-rich B-cell lymphoma in a 69-year-old female is presented. The patient was admitted with a diagnosis of a brain tumor in July 1993 and a month long history of mental deterioration, motor weakness of the right arm and leg, and a tendency toward somnolence. Neurological examination revealed disturbance of consciousness, right hemiparesis, and papilloedema. However, her general physical examination was unremarkable. A CT scan and MR imaging revealed an irregular enhanced mass lesion at the paraventricular deep white matter in the bilateral parieto-occipital lobe. The patient was treated with surgical biopsy of the tumor followed by combined radiotherapy (a total of 50 Gy) and chemotherapy. Following repetitive episodes of remission and exacerbation, the patient expired about seven months after the onset of symptoms. Histopathological diagnosis of the tumor was malignant lymphoma (diffuse medium-sized cell type). In the immunohistochemical study, most of the lymphoma cells had T-cell markers, such as UCHL1. Some of the lymphoma cells were L26-positive. Neither glial fibrillary acidic protein nor neuron specific enolase were reactive with the lymphoma cells. At post-mortem examination, the specimens disclosed diffuse infiltration of medium-sized lymphoma cells. By contrast, most of the lymphoma cells were shown to be positive by the analysis of L26. None of the lymphoma cells exhibited the presence of UCHL1. These immunohistochemical evaluations conform to the criteria of T-cell-rich B-cell lymphoma.