Twenty-three cases of primary brain lymphomas were morphologically studied. Electron microscopy was done in twelve cases and immunoperoxidase reactions for light chains of immunoglobulins in ten cases. The patients were fourteen males and nine females. Except two children, the mean age was 50 years. Clinical features and pre-operative investigations lacked any specificity. Post-operative radiotherapy could be performed in thirteen patients, eleven of them being still alive with a follow-up varying from 2,5 months to 4,5 years. All the other patients persued fulminating course (max: 4,5 months). Tumors were preferentially located in frontal and temporal lobes. On gross examination, well limited tumors were more frequent than ill-defined or purely infiltrating tumors. Microscopically, all the lymphomas were of the diffuse type. Perivascular clusters of lymphoma cells, meningeal and parenchymal infiltrates and sub-ependymal sprouts were found in the peritumoral areas. The lymphomas were cytologically characterized according to the modified Kiel classification (Lennert et al, 1975) using light and electron microscopic data. So were identified thirteen lymphoblastic lymphomas (with one convoluted-cell type), one centroblastic lymphoma, eight immunoblastic lymphomas (two with plasmacytic differentiation). Light chains of human immunoglobulins were immunocytologically demonstrated in six of twelve tumors tested, all the positive cases corresponding to immunoblastic lymphomas. A unique case of primary meningeal Hodgkin's disease was found. These results were compared with the rare previous reports associating these different morphological investigations.