Paratracheal air cyst (PTAC) is a small air collection in the right paratracheal area and mainly diagnosed by computed tomography (CT). Increased with ultrasonographic (US) screening of the thyroid, PTAC can be detected incidentally. However, the US findings of PTAC have not been well described. Herein, we report our experience with a rare instance of a PTAC. A 64-year-old female was referred to our hospital for fine-needle aspiration (FNA) cytology of a thyroid nodule. The lesion was identified as an ovoid, hypoechoic lesion with internal hyperechoic foci, abutting on the inferior pole of the right thyroid lobe. The margin was smooth without hypoechoic rim, which is typical in upper esophageal diverticula. US-guided FNA suggested a benign bronchial epithelial lining cyst. If a hypoechoic neck mass containing air without a thick hypoechoic rim is observed, especially at the right side of the trachea, the possibility of PTAC should be considered.