An overall goal, in healthcare, is the identification and prevention of errors. This goal requires a mechanism for the codification and organization of the published literature related to healthcare errors. While there are a number of limited taxonomies to classify healthcare or medical errors, no single system has widespread acceptance. The goal of this project has been to develop an ontology which could be used for the codification of healthcare⁄medical errors which could act as an organizing structure for those researching this field and to create a standard mechanism to codify errors as a first step in healthcare/medical error prevention and the improvement of patient safety. This paper describes our efforts in developing a comprehensive medical error ontology to serve as a standard representation for medical error concepts gleaned from various existing published taxonomies, and to the ultimate goal of improving patient safety. Eight candidate taxonomies were selected from published literature and merged to create a reference ontology consisting of 12 multi-dimensional axes that encompass all the aspects of a medical error event. Subsequent steps include mapping the reference ontology to the original taxonomies and building a knowledge base of medical error cases. This approach builds on the work which has already been accomplished, but extends it into new domains.