This article describes an unusual clinical-radiographic presentation of a lateral periodontal cyst, as a differential diagnosis of a residual cyst, following the ‘CARE guidelines for case reports’. The radiolucent lesion was identified on the imaging exam of a 53-year-old male patient. Based on radiographic findings and aspiration puncture, the probable diagnosis was a residual cyst; however, histological analysis revealed a thin, non-inflamed fibrous capsule covered by some epithelial layers in most of the lesion. The definitive diagnosis was a lateral periodontal cyst with unusual clinical and radiographic features. The cyst was surgically enucleated and local bone neoformation was observed, with no signs of recurrence after 12 months. The results of this study suggest that a radiolucent lesion, suggestive of a residual cyst or keratocyst in the maxilla, may correspond to a lateral periodontal cyst. In this context, the histopathological analysis of the cyst is essential for the definitive diagnosis. Key words: Cysts, odontogenic cysts, periapical cysts, periodontal cysts.