Cervical thymic cyst is uncommon and usually occurs in the first and second decades. Cervical thymic cyst after the third decade is so rare that it is very difficult to diagnose in spite of its typical location. We present a rare case of cervical thymic cyst in the lower left - anterior of the neck in a 50-year-old woman. It showed well-defined, anechoic cyst on ultrasonography and non-enhancing low attenuation mass on CT. A typical anatomic relationship was noted between the mass and carotid sheath.