A retained drainage tube fragment after surgery is a rare complication with potentials for medical dispute. We report the case of a retained drainage tube fragment in the anterior neck following conventional thyroid surgery. To the best of our knowledge, this is the first report of its kind. A 61-year-old female patient who was found to have a retained Penrose drainage tube after thyroid surgery for a papillary thyroid cancer. The retained tube was detected 18 months after surgery presenting as a palpable neck mass. Neck ultrasonography revealed a hypoechoic lesion with tubular-shaped parallel hyperechoic lines, suggesting a retained drain tube. The lateral soft tissue neck radiograph demonstrated a radio-opaque drain tube in the anterior neck. The fragment of a Penrose drainage tube was neglected first, and then detected as a palpable neck mass 18 months after surgery. Removal of the drainage tube fragment was performed under local anesthesia. After the surgery, the operation site healed without any complications. Although drainage procedure is regarded to be easy, there can be associated complications including retained drain, bleeding, infection, or cosmetic problem. So, clinicians should be aware of rare complications associated with Penrose drainage tubes after thyroidectomy and perform this procedure carefully and gently to avoid them.