The association of medial elbow ganglion cyst with cubital tunnel syndrome has been rarely reported. A 61-year-old man presented with progressive right hypothenar atrophy and paresthesia for 7 months. Ultrasonography and magnetic resonance imaging revealed ulnar nerve entrapment with a cystic ganglion in cubital tunnel. Decompression of ulnar nerve and excision of the ganglion were performed. Motor function of the ulnar nerve showed an improvement four months later after surgery. Because most ganglia are occult, imaging study is warranted especially in case with osteoarthritis. Excision of the ganglion performed concurrently with decompression of the ulnar nerve provide satisfactory results.