Teratoid cysts are rare developmental anomalies of the maxillofacial skeleton that pose significant diagnostic challenges, particularly when extensive and located in the edentulous mandible. Their radiological resemblance to more common cystic lesions can lead to misdiagnosis and suboptimal surgical outcomes. This report presents a 60-year-old female with a 1-year history of pain and swelling in the left mandibular angle. Clinical examination revealed a soft, fluctuant, compressible swelling without purulence. Orthopantomography showed a radiolucent lesion spanning from the mental foramen to the condylar neck, with cortical thinning across the mandibular base. Cone beam computed tomography (CBCT) confirmed a unilocular cystic lesion with buccolingual expansion and a paper-thin cortex. Aspiration yielded white fluid preoperatively and serosanguinous fluid (≈30 mL) on the day of surgery. Under local anesthesia, enucleation was performed following biopsy, and histopathology confirmed a teratoid cyst. The lesion's aggressive radiographic profile in an edentulous mandible underscores the importance of a broad differential diagnosis and meticulous preoperative planning. Conservative surgical management, tailored to the patient's age and bone integrity, resulted in successful healing without pathological fracture. This case highlights the critical need for diagnostic vigilance and individualized treatment strategies in managing rare mandibular cysts.