Introduction: The effort to increase patient safety has become one of the main focal points of all health care professions, despite the fact that, in the fild of dentistry, initiatives have come late and been less ambitious. The main objective of patient safety is to avoid preventable adverse events to the greatest extent possible and to limit the negative consequences of those which are unpreventable. Therefore, it is essential to ascertain what adverse events occur in each dental care activity in order to study them in-depth and propose measures for prevention. Objectives: To ascertain the characteristics of the adverse events which originate from dental care, to classify them in accordance with type and origin, to determine their causes and consequences, and to detect the factors which facilitated their occurrence. Material and Methods: This study includes the general data from the series of adverse dental events of the Spanish Observatory for Dental Patient Safety (OESPO) after the study and analysis of 4,149 legal claims (both in and out of court) based on dental malpractice from the years of 2000 to 2010 in Spain. Results: Implant treatments, endodontics and oral surgery display the highest frequencies of adverse events in this series (25.5%, 20.7% and 20.4% respectively). Likewise, according to the results, up to 44.3% of the adverse events which took place were due to predictable and preventable errors and complications. Conclusions: A very signifiant percentage were due to foreseeable and preventable errors and complications that should not have occurred.