This paper describes the effects of therapeutic electrical stimulation (TES) on the wasting muscles in a patient with amyotrophic lateral sclerosis. The patient is a 47-year-old male, and he has a history of progressive muscle weakness and atrophy, affected more in the right side. Percutaneously indwelling intramuscular electrodes were implanted to the affected muscles in the right upper and lower extremities but no electrode in the corresponding left region. Within a month of TES therapy, a rapid improvement of extremity motion appeared in the TES treated side. Long-term application of TES more than 3 months increased the strength of the muscle which had been evidently weaker than the non-treated side. CT findings of both the upper and lower extremities with TES therapy showed an increase in the density and a reduction in the moth-eaten image. An increase in the thickness of the muscles was also observed in the TES treated side while deterioration was observed in the muscles on the non-treated side.