Ganglion cysts are cystic growths caused by herniation of synovial from joint and tendon sheath them on.Ganglion cysts are the most common soft tissue tumors of the wrist, hand and foot. They are classified as intraosseous, subperiostal and soft tissue cysts according to their anatomic region and origin. Treatment methods are listed such as observation, aspiration, sclerotherapy and surgical excision After the surgery, there is a risk of recurrence by 13–40%. The occurence of hypothenar region ganglion cysts, which cause ulnar nerve entrapment neuropathy by compressing Guyon Canal is not frequent.So we aimed to report a case with a giant ganglion cyst which is localizated in the hypothenar region of the right hand and causes ulnar nerve compression symptoms.