Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic autoimmune disabling neuromuscular disease caused by antibodies against presynaptic voltage-gated calcium channels. It reduces the quantal release of acetylcholine (ACh), causing muscle weakness, reduced or absent reflex and dysautonomia. About half of LEMS patients have associated small cell lung cancer. For symptomatic treatment, ami-fampridine (3, 4-diaminopyridine [3, 4-DAP]) is ideal because it increases the release of ACh at the presyn-aptic membrane. After the first use of 3, 4-DAP in LEMS patients in the 1980s, 136 LEMS patients were treated with amifampridines in the open-label studies and 208 patients in the eight randomized studies. These studies showed that amifampridine is the most effective drug for symptomatic treatment in LEMS. Now, 3, 4-DAPP (3, 4-DAP phosphate) is approved for adult LEMS patients and 3, 4-DAP for pediatric patients. The recommended dose is 80 mg a day, divided 3 or 4 times a day. Side effects are usually mild, and the most frequently reported are paresthesia.