Introduction: Odontogenic cysts constitute a group of frequent intraosseous lesions characteristic in the maxillary bones and one of the main causes of the destruction of these bones. In Chile there are no retrospective studies of these lesions as a whole. Objective: The purpose of this study is to determine the frequency of these lesions in so far as they were diagnosed and registered in the Referral Institute for Oral Pathology (IREPO) of the University of Chile in two age groups as well as to analyze and to compare the data obtained with the data published in previous studies. Material and Method: We studied the records from IREPO of the University of Chile for the period between 1976 and September, 2004; and we determined the frequency according to age, gender and site of each of these lesions. We compare two age groups: younger than or equal to 15 years old and older than 15 years old. Those cases in which the information did not suffice for the purposes of analysis were not considered. All the histological slides were reclassiffed according to the diagnostic criteria included in the Histological Typification of the World Health Organization. Results: We found 2.944 odontogenic cysts (OC), of which 1.935 (65.7%) were inflammatory cysts and 1.009 were developmental cysts. Out of this total, there were 1.554 cysts (52.8%) in men and 1.390 (47.2%) in women. The most frequent cysts were 1.494 radicular cysts (50.7%), 546 dentigerous cysts (18.5%), 421 keratocysts (14.3%) and 328 residual cysts (11.1%). These four varieties represent 94.7% of the OC , that is, 2789 cases. In the population younger than or equal to 15 years of age the developmental cysts (354 cases) are more frequent than the inflammatory cysts (155 cases), the most frequent being dentigerous cysts (240 cases).