The case of a 17-year-old boy who had been well until the age of four when progressive stiffness of lower limbs developed is reported. Soon walking became dificult and on his thighs, buttocks and calves one could notice the appearance of myokymia. Painful and intermittent spasms were often present speccially after physical strain. This was followed by profuse sweating. Strenght was normal but muscle relaxing was slow mainly in the quadriceps. The familiar history for neuromuscular pathology was negative. Muscle enzymes, thyroid function tests were within normal limits and muscular biopsy showed no abnormalities. The EMG disclosed a permanent spontaneous activity, more evident in the quadriceps, which was normal in shape, amplitude and duration. In association to this activity multiplets discharges and low motor units were also observed; an interferencial pattern appeared at maximum contraction but the multiplets and low motor units potentials kept on showing even though voluntary muscular activity had ceased. The therapeutic essay with carbamazepin had a dramatic effect upon the course of the patient's conditions. He showed a great improvement with this drug and today leads a normal life being able even to play soccer and ride a bycicle. An interesting remark which should be done is the fact that the flexion of the neck inhitibs the quadriceps myokymia whereas the extension makes them to appear and even worsen. Unfortunately is was not possible to carry out a more accurate investigation concerning electropharmacology and hystopathology as the patient was uncooperative and refused to undergo such examinations. However the authors believe that this clinical picture can be considered as a case of "continous muscle-fibre activity" due to the great similarity it bears to the cases related by Isaacs in 1961. An extensive review concerning the pertinent literature has been done.