Novel efficient and aggressive treatment protocols for primary CNS lymphomas have resulted in an increasing number of long term survivors. Follow up data show that in a substantial fraction of these patients, treatment benefits are overshadowed by neurotoxic sequelae. Neurotoxicity especially affects the older age group, presenting as cognitive dysfunction, ataxia or dementia as a consequence of leukoencephalopathy and brain atrophy. The combination of radiotherapy and chemotherapy seems to be particularly hazardous, though data are too sparse to draw any definite conclusions yet. Long term follow up of patients included in clinical studies therefore should not only evaluate survival or time to tumour progression, but also serial neuropsychometric evaluation and quality of life assessment.