A 52-year-old male developed hypertrophy of the right calf after several bouts of right lumbar pain with sciatica. Electromyography disclosed evidence of demyelination in the territories of the right S1 and S2 roots. Microscopic studies showed both atrophic muscle fibers scattered among fibers of normal caliber and a large number of hypertrophic fibers. Post-sciatica hypertrophy of the calf is a true muscle hypertrophy with muscle weakness. Electromyography may show unusual tracings with repeated complex bursts or continuous activity of motor units. Muscle enzyme levels may be elevated. The size of hypertrophied fibers varies across cases. The cause of the muscle fiber hypertrophy may be either stretching due to the action of antagonists or unusual electrical activity.