Zenker's diverticulum is rarely known to be an impediment to the diagnosis and surgical procedure for thyroid disease. In this report, we discuss a rare case of pre-operative diagnosis of asymptomatic Zenker's diverticulum and surgical treatment of the disease during thyroidectomy. A 48-year-old male was referred to our hospital with multiple thyroid nodules confirmed to be papillary thyroid cancer. Pre-operative ultrasonography and computed tomography scan findings suggested the presence of a left Zenker's diverticulum. The left pharyngeal pouch was treated by reinforcing the overlying soft tissue during thyroidectomy, without structural injury to the recurrent laryngeal nerve. We report this case with a focus on the considerations during the pre-operative diagnosis and precautions to be taken during surgery, such as the distorted path of the recurrent laryngeal nerve and manipulation of the diverticulum.