Paraneoplastic nervous system syndromes are being identified with increasing frequency because of greater physician awareness and the availability of serodiagnostic tests for some syndromes. Frequently, paraneoplastic syndromes develop in the setting of an indolent, limited stage, or otherwise occult malignancy. As a result, the paraneoplastic disorder often becomes the most disabling part of a patient's disease. Effective treatment appears to require early identification. For these reasons, the ability to diagnose a paraneoplastic syndrome, follow its course, and treat it successfully are important. The authors describe four patients with neurologic paraneoplastic syndromes and identical magnetic resonance imaging abnormalities. Three patients responded to immunosuppressive or immunomodulatory therapy, and in one, corresponding radiographic improvement was documented. Strategies for early diagnosis and options for treatment of paraneoplastic nervous system disorders are discussed.