Killian-Jamieson diverticulum is a rare hypopharyngeal diverticulum, less commonly encountered compared with Zenker's diverticulum. These hypopharyngeal diverticula that cause dysphagia often mimic a thyroid tumor incidentally detected on neck ultrasonography. However, to our knowledge, Killian-Jamieson diverticula complicated by a thyroid tumor have not been previously described. We experienced a rare case of bilateral Killian-Jamieson diverticula synchronously complicated by a thyroid adenoma in a 74-year-old woman who became aware of dysphagia and a tumor in the left side of her neck. Pharyngoesophagography revealed bilateral diverticula protruding from the lateral wall of the esophagopharyngeal junction, but the appearance of the cricopharyngeal bar representing the cricopharyngeus muscle above the diverticula had become unclear because the thyroid tumor was pressing on the diverticula and the cervical esophagus. However, the diverticula were diagnosed as Killian-Jamieson diverticula because cervical computed tomography showed bilateral diverticula arising from the cervical esophagus just below the level of the cricoid cartilage, and operative finding showed that the diverticula were located above the upper esophageal longitudinal muscle. Radiographic imaging is useful for diagnosis as cause of dysphagia and cervical tumor.