Hereditary neuralgic amyotrophy (HNA) belongs to the group of recurrent focal neuropathies, the other major representative being hereditary neuropathy with liability to pressure palsies. The search for the HNA gene has now focused on a locus on chromosome 17q24-q25. Most HNA families show linkage to this locus, but recent evidence indicates that HNA is genetically heterogeneous. Detailed analysis of these unlinked families has broadened our perception of the HNA phenotype, and currently two different clinical courses can be discerned: the classical relapsing-remitting course and a chronic undulating course. After 5 years of molecular genetic research, this disease remains enigmatic. At present, we can only speculate how such very diverse stimuli as immunizations, childbirth, infections, strenuous exercise, and immobilization can trigger painful attacks of brachial plexus palsies in genetically susceptible individuals.