Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that causes episodes of focal demyelinating neuropathy following minor trauma to peripheral nerves. We assign the HNPP locus to chromosome 17~ 11.2 and demonstrate the presence of a large interstitial deletion associated with this disorder in three unrelated pedigrees. De novo deletion is documented in one pedigree. The deleted region appears uniform in all pedigrees and includes the gene for peripheral myelin protein 22 (PMP-22j, suggesting that underexpression of PMP-22 may cause HNPP. The deletion in HNPP spans approximately 1.5 Mb and includes all markers that are known to map within the Charcot-Marie-Tooth neuropathy type 1A (CMTl A) duplication. Furthermore, the breakpoints in HNPP and CMTl A map to the same intervals in 17~ 11.2, suggesting that these genetic disorders may be the result of reciprocal products of unequal crossover.