Results of clinical, electrophysiological and morphological examination, were presented in 19 patients from 8 families with hereditary motor-sensory neuropathy type I (HMSN type I) with 17p11.2-12 duplication (i.e. CMT IA). The course of the disease was rather mild, slowly progressive. Generalized demyelinating lesion of peripheral nerves was found on EMG examination, with median nerve conduction velocity between 10-20 m/s and very prolonged F wave latency. Sural nerve biopsy was characteristic of chronic demyelinating process. Phenotypic characteristics of our HMSN type I patients shows clinical, electrophysiological and morphological homogeneity, however there are some data from literature indicating possibility of intrafamilial and interfamilial variability.