Definition and backgroundRandomized controlled trials (RCTs) provide the highest level of evidence in clinical research and are the foundation of evidencebased medicine. 1 However, ongoing challenges continue to face surgical trials. These include the small number of studies relative to the number of important questions, the fact that many studies fail to recruit, as well as the uncertain applicability of outcome data to real-world practice due to often stringent eligibility criteria. 2 In addition, a major factor with limiting trial initiation is the cost of traditional RCTs, a significant component of which is associated with data collection.Clinical registries are databases that collect patient, treatment and outcome data in routine care, potentially supporting a large range of research and audit projects. An emerging clinical trial methodology, the registry-based randomized controlled trial (RRCT), has been introduced to reduce barriers to opening trials, particularly to reduce costs and to facilitate the enrolment of more real-world patients. This pragmatic study design utilizes registry databases to collect trial outcome data, with patients randomized between current standard-ofcare treatment options. 3,4 Registry databases can also be used to identify trial candidates. With typically broad entry criteria RRCTs support high-quality outcome data being captured in the clinical registry, obtained from enrolled patients representative of the "real world" population.