A patient with paraneoplastic encephalomyelitis (PEM) and small cell lung cancer had a clinical presentation of acute polyneuritis. The patient had an antibody (anti-Hu) restricted to nuclei of neurons identical to that reported in patients with subacute sensory neuronopathy and lung cancer. This finding further supports the hypothesis that PEM and subacute sensory neuronopathy are closely related disorders of autoimmune origin. PEM should be considered in patients with small cell lung cancer and clinical features limited to the peripheral nervous system.