The ameloblastoma is a locally aggressive odontogenic tumour that has high recurrence rates. It rarely presents a histological aspect similar to the odontogenic keratocyst, because of the presence of keratinised areas. This study aimed to report a case of ameloblastoma in the mandible, diagnosed and treated incorrectly as an odontogenic keratocyst because of unusual macroscopic characteristics and rare histological aspects that impaired a correct diagnosis. Case report: A 57-year-old female

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... year-old female patient, presenting an asymptomatic lesion at the left mandibular angle, was treated by incisional biopsy and decompression. The histological sections showed an aspect suggesting odontogenic keratocyst. At the 3-year postoperative period, the patient returned with a new lesion on the left side of the mandible and was then subjected to curettage. The histological sections showed a pattern of ameloblastoma and, because of this, the patient remained with a 6-month follow-up. At the 4-year postoperative period after the second operation, the patient returned with a new recurrence. The biopsy showed an ameloblastoma and the patient was submitted to mandibular resection and reconstruction as treatment. After the final procedure, the recovery was uneventful and the patient is now undergoing a postoperative period of four years, without recurrences. Conclusion: This case highlights the importance of carrying out a proper biopsy and an adequate examination by a specialised professional, because of the possibility of atypical lesions occurring restricted to the head and neck region.