Primary intracranial T-cell lymphoma is a very rare clinical entity, and only limited biological studies of this disease have been undertaken. A tumor specimen from a patient with a primary leptomeningeal and perivascular presentation of a T-cell lymphoma was analyzed using cellular and molecular techniques. Frozen sections of the sample were examined by immunohistochemical techniques using monoclonal antibodies to phenotypic marker antigens expressed on human lymphoid cells. Intercellular adhesion molecules expressed on the tumor were studied, as was expression of messenger ribonucleic acid (mRNA) transcripts of the T-cell receptor variable alpha and beta chain genes. The immunophenotypical analysis of lymphoma revealed that the tumor expressed CD2, CD3, CD4, CD5, CD25 and HLA-DR. In addition, all of the adhesion molecules studied (ICAM-1, LFA-3, VLA-1, CD11a, CD11b, and CD11c) were detected on the cell surface. Polymerase chain reaction amplification of mRNA from the tumor demonstrated 10 V alpha and three V beta T-cell receptor subfamilies, indicating that this tumor was a low-grade well-differentiated helper type of peripheral T-cell lymphoma of the central nervous system. In addition, the tumor was derived from multiple T-cell lineages.