A 33-year-old male had complained of a painless mass above his right knee joint for more than three years. Physical examination revealed a firm, mobile, non-tender mass superior-lateral to his right knee joint. Magnetic resonance imaging showed a cystic lesion within the vastus lateralis muscle without communication to the knee joint. After excision of the mass, pathological report of the specimen showed a ganglion cyst without lining cells. Based on its anatomic location and histology, the final diagnosis was intramuscular ganglion cyst of the quadriceps muscle.