AN UNUSUAL CASE of leg pain and atrophy in a patient with gastrocnemius due to tibial nerve branch compression by a Baker's cyst is presented. The clinical findings and electrodiagnostic studies were supportive of isolated medial gastrocnemius denervation. Treatment by synovectomy along with decompression of the branch of the posterior tibial nerve to the medial head of the gastrocnemius muscle resulted in clinical improvement. No other cases of such selective branch compression have been previously reported.