The clinical, genetic and electrophysiological study of 3 patients with an association of a neuronal form of Charcot-Marie-Tooth Disease (CMTD) with a syndrome of continuous motor unit activity (CMUA) are reported, with light and electron microscopy of muscle and sural nerve biopsies in 2 patients. The unusual clinical features of CMTD were associated with fasciculation, cramps, myokymia, impaired muscular relaxation and percussion myotonia with their electromyographic (EMG) correspondent, responsive to valproic acid (VPA) therapy. In Case 3, an important muscle hypertrophy which was confirmed by morphometric data, was noted in addition. Nerve biopsy and electrophysiological findings indicated that axonal degeneration with secondary demyelination and remyelination underlie the hereditary motor and sensory neuropathy (HMSN) in our patients. The hyperexcitability and hyperactivity of peripheral motor axons probably induced by the hereditary neuropathy may, in this instance, be the causative condition of the syndrome of CMUA in our patients.