A case is reported of a 40 year old woman treated with intraventricular IL-2 for leptomeningeal disease who developed progressive cognitive dysfunction. This deterioration started 3 months post-treatment and worsened over the ensuing 4 years. MRI revealed white matter abnormalities that were not present on the pretreatment scan. Although free of disease, the patient has a subcortical dementia and is unable to work. The potential for progressive brain injury and subsequent disability related to intraventricular IL-2 therapy is discussed.