Hereditary neuralgic amyotrophy with predilection for the brachial plexus (HNA) and hereditary neuropathy with liability to pressure palsies (HNPP) are autosomal dominant disorders associated with episodic, recurrent brachial neuropathies. HNPP is associated with a deletion or abnormal structure of the PMP22 gene on chromosome 17p11.2-12. The genetic locus for HNA is unknown. To address the possibility that HNPP and HNA might be identical disorders or allelic variations at the same locus, we investigated three HNA pedigrees with markers from the HNPP region. We did not find the 17p11.2-12 deletion associated with HNPP, nor an abnormality in PMP22 structure with HNA. This analysis provides genetic evidence, in addition to that suggested by the clinical, electrophysiologic, and pathologic differences, that HNA and HNPP are distinct disorders.