An ameloblastoma is a benign, yet locally aggressive odontogenic tumour. The vast majority (80%) of ameloblastomas arise in the mandible, and unicystic ameloblastomas are commonly found in relation to an unerupted lower third molar. We present the case of a 39-year-old patient with an incidental finding of an enlarged dental follicle around an unerupted lower third molar that progressed to an extensive unicystic ameloblastoma. This ameloblastoma was decompressed and marsupialized before enucleation to reduce the risk of pathological fracture due to the extensive size of the tumour. CPD/Clinical Relevance: The case is relevant to general dental practitioners when considering monitoring dental follicles of unerupted teeth because the enlarged dental follicle described progressed to an extensive odontogenic tumour.