Lambert-Eaton myasthenic syndrome is a rare autoimmune neuromuscular and autonomic disease that produces fluctuating muscle weakness, hyporeflexia, and autonomic dysfunction, and often is associated with small-cell lung cancer. The pathophysiology is understood quite well; antibodies to voltage-gated calcium channels in motor and autonomic nerve terminals disrupt calcium influx and reduce acetylcholine release. The diagnosis may be suspected clinically, but must be confirmed with electrophysiologic testing. Initial and then periodic screening for malignancy is essential. Tumors other than small-cell lung cancer occasionally are found. Effective tumor treatment may induce remission. Active disease may respond to agents that enhance neuromuscular transmission or to immunosuppression. Combined therapy frequently is needed and control is often marginal despite this. It is expected that availability of 3,4-DAP will improve significantly the response to treatment in most patients.