According to the World Health Organization's classification given in 1992, the odontogenic cysts associated with inflammation are: radicular cyst, residual cyst and paradental cyst. 1 Radicular cysts (RCs) are the most common inflammatory odontogenic cysts and arise from the epithelial residues in the periodontal ligament known as the cell rests of Malassez, which undergo inflammation following pulpal necrosis. 2 Residual radicular cysts (RRCs) also called as residual cysts, represent 10-18% of inflammatory odontogenic cysts and commonly present between the 4th-6th decade of life. 1,3 Maxilla is more commonly involved (66.2%), predominantly the posterior areas. Males are more commonly affected in a 3:2 ratio. 3 RRCs are believed to originate from a RC that is inadvertently left behind entirely or in fragments, following extraction of the involved tooth. 1 However, the identity of these cysts is still debated as few authors believe that majority of them represent slowly resolving RCs. 4 Compared to other odontogenic cysts, the attention paid to the RRCs within literature is significantly less. 5 Although these cysts are slow growing and are usually found incidentally, they have a potential to reach massive sizes, displace adjacent structures and transform into benign or malignant tumours. 6 This article reviews the literature available on the etiopathogenesis, presentation, management and prognosis of RRCs along with a report of a large residual cyst in right maxilla, displacing the maxillary sinus. The cyst was filled with brownish red viscous content which is uncommon. The lesion was enucleated and no post-operative complications were observed.