Neurolymphomatosis (NL) is a rare clinical entity. The International Primary CNS Lymphoma Collaborative Group retrospectively analyzed 50 patients assembled from 12 centers in 5 countries over a 16-year period. NL was related to non-Hodgkin lymphoma in 90% and to acute leukemia in 10%. It occurred as the initial manifestation of malignancy in 26% of cases. The affected neural structures included peripheral nerves (60%), spinal nerve roots (48%), cranial nerves (46%), and plexus (40%) with multiple site involvement in 58%. Imaging studies often suggested the diagnosis with 77% positive magnetic resonance imaging, and 84% (16 of 19) positive computed tomography-positron emission tomography studies. Cerebrospinal fluid cytology was positive in 40%, and nerve biopsy confirmed the diagnosis in 23 of 26 (88%). Treatment in 47 patients included systemic chemotherapy (70%), intra-cerebrospinal fluid chemotherapy (49%), and radiotherapy (34%). Response to treatment was observed in 46%. The median overall survival was 10 months, with 12- and 36-month survival proportions of 46% and 24%, respectively. NL is a challenging diagnosis, but contemporary imaging techniques frequently detect the relevant neural invasion. An aggressive multimodality therapy can prevent neurologic deterioration and is associated with a prolonged survival in a subset of patients.