The inflammatory paradental cyst has previously been described as the collateral inflammatory cyst, the inflammatory lateral periodontal cyst, the paradental cyst, or the mandibular infected buccal cyst. Clinical, radiographic, and histologic features of 29 inflammatory paradental cysts diagnosed over a 5-year period were studied. The cysts occurred in relation to a partly or fully erupted tooth with a vital pulp. Twenty-seven of the cysts were located in the mandible and the remaining two in the maxilla. The mandibular cysts were in all cases associated with a molar. The observation that the cysts are diagnosed within a few years after tooth eruption and the demonstration of a statistically significant difference (p = 0.001) in age distribution and in the type of tooth involved suggest that eruption is important for the development of the cysts. The consistent finding of a hyperplastic, nonkeratinized stratified squamous epithelium with an intense inflammation in the connective tissue is in accordance with the hypothesis that inflammation is important for the development of these cysts.