The case of a 17 years-old woman, with clinical findings of meningites, without identification of a pathogenic agent is reported. The pacient received treatment for tuberculous and fungi meningites. In the clinical course were found neoplasic cells in the spinal fluid. Despite the radiologic investigation, the original site of the tumor was not found in life. In the post-mortem examination, a small tumor was discovered in the 4th ventricle. The hystologic examination revealed a primary central nervous system lymphoma, diffuse infiltration of the meninges by tumor cells and proliferation, into the central nervous system through the Virchow-Robin space. The clinical course, laboratory investigation and anatomical findings of the tumor are presented. A short revision about the pathogenesis of neoplasic meningites and primary central nervous system lymphoma is made.