A 5.5 year old Turkish boy who suffered from progressive muscle stiffness was diagnosed as having continuous muscle fiber activity syndrome. Electromyography showed continuous motor neuron activity at rest and following intravenous injection of diazepam. Peripheral nerve block, spinal and general anesthesia diminished the spontaneous activities. The clinical and electrophysiological findings of our case were compared to the previously reported cases with emphasis on the heterogeneity of the syndrome.