<jats:p><jats:italic>Background</jats:italic>. A radicular cyst is the most common odontogenic cyst of inflammatory origin. Radiographically, it commonly demonstrates clear unilocular radiolucency; radicular cysts with multilocular radiolucency are quite rare. <jats:italic>Case Presentation</jats:italic>. A 64-year-old Japanese man who presented with a bilocular radiolucent lesion in his left mandible was referred by a dental clinic to our oral and maxillofacial surgery department. He had no particular subjective symptoms. Orthopantomography and computed tomography (CT) revealed an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mn>18</mml:mn><mml:mtext> </mml:mtext><mml:mtext>mm</mml:mtext><mml:mo>×</mml:mo><mml:mn>15</mml:mn><mml:mtext> </mml:mtext><mml:mtext>mm</mml:mtext></mml:math> lesion with well-defined bilocular radiolucency in the left mandible expanding from the distal side of a canine tooth to the bottom of the 2nd premolar. The lesion included the roots of the 1st and 2nd premolars. The root of the 2nd premolar showed knife-edge resorption. Although the 1st premolar was nonvital, the 2nd premolar was a vital tooth. As differential diagnoses, a radicular cyst, ameloblastoma, odontogenic keratocyst, pseudocyst, and others might be considered. We performed a total resection of the bilocular lesion and diagnosed the lesion as a radicular cyst with tooth structure components inside. The tooth structure components represented lamellar structures of cementum; they were located only in the proximal part (under the 1st premolar) of the lesion. The distal part of the lesion presented distinctive inflammation without tooth structure components. <jats:italic>Conclusion</jats:italic>. We encountered a rare case of a bilocular radicular cyst with tooth structure components inside.</jats:p>