Ameloblastoma is the most common odontogenic tumor and generally arises inside the bone. It is locally invasive, typically localized at the angle of the mandible. The nature of this lesion is benign. It is usually an asymptomatic, slow-growing, and painless tumor. Treatment depends on the type and histopathological subtype of the lesion.Due to the WHO classification from 2022, 5 basic types of ameloblastoma are discerned: ameloblastoma - unicystic type, ameloblastoma - extraosseous/peripheral type, ameloblastoma - conventional (in classification from 2005 solid/multicystic type), adenoid ameloblastoma and 5) metastasizing ameloblastoma. The most common type is the conventional type, and then the unicystic type. Treatment is primarily surgical. We present a rare case of a patient with unicystic ameloblastoma as an accidental discovery during the surgical removal of the lower third molar and a 20-year follow-up. This case highlights the importance of diagnostic methods and difficulties in the treatment of a patient with ameloblastoma.