PURPOSE: The purpose of this study was to characterize a population of oligodontia patients and identify patterns of tooth agenesis. MATERIALS AND METHODS: A total of 116 patients with nonsyndromic oligodontia were studied, and the Tooth Agenesis Code (TAC) per quadrant was calculated. Oligodontia was defined as the congenital absence of 6 or more permanent teeth, excluding the third molars. The TAC is a unique number, consistent with a specific pattern of tooth agenesis. The authors suggest the use of an overall TAC with which the dentition throughout the mouth can be presented by a single number. Frequency analysis was used to study the prevalence of various patterns. RESULTS: There was a great diversity of TACs. In the maxilla, agenesis of both premolars and the lateral incisor or the presence of only the central incisor and first molar were the most common patterns. In the mandible, agenesis of the second premolar or both premolars occurred most frequently. CONCLUSIONS: No single pattern of agenesis occurred more than twice when the full mouth was viewed. Hence, the presentation of the dentition in oligodontia is very heterogeneous. Evaluation of treatment strategies in oligodontia patients is a methodologic challenge because homogenous, comparable subgroups of patients are not available.