Mandibular swellings may occur as a result of many benign lesions of odontogenic or non-odontogenic origin. Ameloblastomas are benign tumours of odontogenic origin, whose importance lies in its potential to grow into enormous size with resulting bone deformity, it is a slow-growing, persistent, and locally aggressive neoplasm. The unicystic ameloblastoma (UA) represents an ameloblastoma variant, presenting as a cyst clinically and radiographically, but showing typical ameloblastomatous epithelium lining histologically. It commonly occurs in second and third decades of life and is rare in children under 12 years of age, and better response to conservative treatment. It shares many clinical and radiographic features with odontogenic cysts/tumours and/or periapical disease of endodontic origin. Reported here is an unusual case of unicystic ameloblastoma involving the crown of an unerupted mandibular first premolar in a 9-year boy in an uncommon location, which was misdiagnosed as periapical lesion of inflammatory origin clinically, and as a dentigerous cyst radiographically. This highlights the importance to routinely submit the removed surgical specimen for histopathological examination.