The risks of endoscopy procedures are likely affected by the competence of the endoscopist and the team (nursing, anesthesia, and technicians), the details of the specific procedure being performed, and the patient's anatomy, demographics, and health status. In 2008, the American Society for Gastrointestinal Endoscopy (ASGE) convened a workshop to recommend a lexicon to define and describe the adverse events (AEs) (previously commonly referred to as complications) that can result from endoscopy procedures. 1 One additional goal of this workshop was to standardize the reporting of factors that may predict AEs, in clinical practice and in research. This list of such factors might enable the creation of risk strata (allowing comparison of AE rates by risk groups). In addition, AE rates among different groups of endoscopists and different groups of patients might be more appropriately compared by strata. Last, prospective risk assessment might enhance the quality of informed consent and facilitate decisions regarding procedural appropriateness.As stated in part I, the aim of this 2-part article is to summarize the body of work that has been published on this topic and to suggest the types of risk factors that need to be considered for inclusion in endoscopy reporting/database systems. Possible, but unproven, risk factors were also considered to guide further research into candidate factors and their relationship with AEs. Establishing and recording the competency of the team are beyond the scope of this article.AEs are often organized by type of event (eg, cardiopulmonary, bleeding, perforation). However, their frequency and type clearly vary by procedure (the risks of colonoscopy are different than those of ERCP), and some events (pancreatitis, infection) rarely or never apply to some procedures. Equally, the factors that predict those AEs also vary among procedures (eg, demographics may predict post-ERCP pancreatitis, but may have little influence on EGD complications).Because many noncardiopulmonary AEs are closely linked to the type of intervention (eg, bleeding or perforation, related to polypectomy), each procedure (eg, colonoscopy, upper endoscopy) would have to be discussed separately under each AE heading. For a more efficient presentation of the data, we elected to discuss them organized by procedure type rather than by AE type. In contrast, most predictors of cardiopulmonary AEs are patient-centered factors and do not vary significantly from procedure to procedure (although admittedly procedural complexity and duration may influence event rates). In addition, comorbidities do not generally predict the noncardiopulmonary events. Therefore, the cardiopulmonary AEs and their predictors, which are relatively constant across procedure types and which require a discussion of the various comorbidity indices, are discussed separately from the other AEs and their potential predictors in part I of this 2-part article. Part II discusses predictors of noncardiopulmonary events and contains a summary and final recommen...