This case report demonstrates an unnecessary endodontic treatment of teeth with florid cemento-osseous dysplasia (FCOD) due to a misdiagnosis as periapical pathosis and emphasizes the importance of correct diagnosis to avoid unnecessary treatment. A 30-year-old woman was referred to our institution for apicoectomies of the mandibular left canine and both the lateral incisors. The periapical lesions associated with these teeth had failed to resolve after root canal treatment over a 3-year period. Radiographic examinations revealed multiple lesions on the right canine, the second premolar, and both first molars as well as the anterior region of the mandible. Based on clinical, radiographic and histological evaluations, the patient condition was diagnosed as FCOD. The patient has been monitored for 2 years. To avoid unnecessary invasive treatment, accurate diagnosis is essential before treatment is carried out in managing FCOD.