Cervical thymic cysts are rare embryonic remnants that develop along the course of thymic migration in the neck. They usually occur during infancy and childhood, and they are extremely rare in adults. We report a case of cervical thymic cyst in a 53-year-old man. The patient presented with a small mass of the thyroid gland and a cystic mass at the left level II area of the neck. On histopathology, the thyroid mass was identified as a papillary carcinoma and the left-sided neck mass was diagnosed as a cervical thymic cyst lined with nonkeratinizing, flattened squamous epithelium. The cyst wall contained atrophic thymic tissue composed of lymphoid cells, epithelial cords, and Hassall corpuscles. Although it is rare, cervical thymic cyst should be considered in the differential diagnosis of a lateral cystic neck mass in an adult.