We report an autopsy case of preclinical primary central nervous system (CNS) lymphoma. The case was an 89-year-old female who died of rupture of a thoracic aortic aneurysm. No neurological abnormalities were found throughout our clinical observation. Serum anti-human T-cell leukemia virus type 1 and anti-human immunodeficiency virus were negative. Grossly, the brain was normal except for a small solid tumor, 6 by 6 by 2.5 mm, in the lateral ventricular wall at the left hippocampal fimbria, and multiple smaller disseminated nodules. Histological examination revealed multiple microscopic disseminated foci throughout the brain, including the cerebral subcortical white matter, basal nucleus, thalamus, brainstem and cerebellum. Histological classification is of lymphoblastic type non-Hodgkin's lymphoma of high-grade malignancy. Lymphoma cells are positive for leukocyte common antigen and L-26, indicating a B cell phenotype. In situ hybridization with Epstein-Barr viral probes is negative. It is concluded that this case may represent a relatively early preclinical stage of multifocal type of primary CNS lymphoma.