Objective: To determine the range of phenotypic expression in individuals with hereditary neuropathy with liability to pressure palsy (HNPP) with the chromosome 17 deletion. Methods: Twenty-one patients from 10 families were studied. Genetic testing was performed in at least one member of each family. Every patient was examined clinically, electrophysiological data was available in 18 patients, and a sural nerve biopsy was performed on 4 patients. In addition, a patient symptom questionnaire was administered over the telephone to identify symptomatic individuals from the at-risk population. Results: The identified phenotypes were those of compressive neuropathy, symmetric peripheral neuropathy (often misdiagnosed as Charcot-Marie-Tooth neuropathy), acute brachial paralysis, and confluent mono-neuropathy multiplex. Many individuals were oligosymptomatic and these formed the majority of undiagnosed patients. Conclusions: The presence of mild symptoms and the marked phenotypic variability of the disease result in underdiagnosis of HNPP.