Objective: To report the occurrence of life-threatening poly- neuropathy in association with renal cell carcinoma. Methods: Case report and review of the medical literature. Results: A 65-year-old man developed a fulminant, life-threatening sensory motor polyneuropathy several months before renal cell carcinoma was identified. Dramatic symptomatic improvement ensued after treatment with intravenous immunoglobulin, although the patient succumbed to complications of the tumor years later. Conclusions: Chronic sensory motor polyneuropathy is a known paraneoplastic syndrome associated with renal cell carcinoma. This report emphasizes that in rare conditions, the polyneuropathy could take an acute demyelinating form, which is important for clinicians to recognize.