Ganglion cyst is considered to be a usual cause of peripheral nerve compression. In this report, we present a rare case of ulnar nerve compression by a multi-septated ganglion cyst in the cubital tunnel. A 33-year-old left-handed male amateur tennis player developed progressive numbness and weakness in his right elbow, forearm, and hand for 1 year. Decrease of grip power was apparent in left hand. Clinical examination revealed a cystic mass at the posterior side of the elbow. Magnetic resonance imaging identified a ganglion cyst at the elbow. During surgery about 3 cm diameter epineural ganglion was observed compressing the ulnar nerve and was excised using microsurgery techniques. Three months postoperatively, the clinical recovery of the patient was very satisfactory and he restored his original performance in tennis match.