Initial enthusiasm about the ability of the World Health Organization's surgical safety checklist to prevent harm was tempered by a subsequent study that failed to improve clinical or safety outcomes. The conflicting results of surgical checklist studies have led to concerns that checklists may lack effectiveness when care is of relatively high quality at baseline, and that poor implementation can hinder their use. In this study, the WHO checklist proved successful at improving safety outcomes when implemented across five surgical services at two academic hospitals in Norway. The checklist's success in this rigorously designed and analyzed study was likely attributable to the institution having followed a structured implementation process that had been previously demonstrated to improve safety culture in the operating room. The controversy around surgical safety checklists is discussed in a recent AHRQ WebM&M interview.