A case of a 35-year-old woman presenting infratentorial CNS lymphoma is reported. In 1990 she complained of diplopia, blurred vision and left horizontal nistagmus. An MRI disclosed a lesion in the medulla, pens, and cerebellar vermis and peduncles. Although no treatment was administered, a later RM[ showed less extension of the tumor. One year after clinical diagnosis, she received corticosteroids; during the second year a stereotaxic biopsy of the cerebellar lesion was done showing a diffuse B cell non-Hodgkin's lymphoma. A whole brain irradiation was given (50 Gy). She did well for five years, and remains alive (79 months).