Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disease characterized by recurrent episodes of acute nerve palsies. We performed a clinical, electrophysiologic, and molecular study of 13 French families with HNPP associated with a chromosome 17p11.2 deletion in 36 individuals. There were electrophysiologic abnormalities in all symptomatic (n = 28) and asymptomatic (n = 8) deletion carriers, even in childhood. Bilateral delayed distal motor latency of the median nerve at the wrist, reduced sensory velocity in the palm-wrist segment, and delayed distal motor latency or reduced motor velocity in the peroneal nerve was diagnostic in at-risk relatives. This large series confirms the reliability of molecular analysis combined with a simplified electrophysiologic examination for the diagnosis of HNPP associated with 17p11.2 deletion.