The Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease of peripheral cholinergic transmission that results in muscle weakness and autonomic dysfunction, due to impaired acetylcholine release. A review of available clinical information indicates that 3,4-diaminopyridine (3,4-DAP) used either alone or in conjunction with other therapies was effective in treating the motor and the autonomic deficits in patients with primary and paraneoplastic LEMS of varying degrees of severity. A survey of the medical literature indicates that about 150 patients have been treated worldwide with 3,4-DAP. The general view is that 3,4-DAP is well tolerated in short- or long-term treatments, with only mild side effects. 3,4-DAP is an orphan drug approved for clinical use in many european countries that lacks adoptive parents because its exploitation is not profitable.