The retrocuspid papilla (RCP) is a poorly recognized entity. In one part of our study, we found 10 cases of lesions clinically compatible with RCP in 1150 consecutively examined patients. In another part of the study, we found 15 cases of RCP in more than 2000 consecutive cases of oral mucosal hyperplasia submitted as surgical biopsies during 1989-92. The lesions were situated in the attached gingiva, lingual to the two mandibular canines, often bilaterally. They were covered by normal pink mucosa with a size and a height each of 2-3 mm. Histologically, the RCP was a broad-based, often downfolded hyperplasia, covered with a parakeratinized epithelium of normal thickness. The rete pegs were often elongated and blunt, frequently bent inward toward the center. The lamina propria was mostly composed of a loosely arranged, delicate, fibrous connective tissue. The lesions could be classified into two groups by the presence or absence of stellate and occasionally multinucleated fibroblasts. Immunohistochemical staining with an FXIIIa antibody disclosed a population of reactive spindle-shaped cells, mainly localized in the connective-tissue papillae. These cells may be of pathogenetic importance.