Root cause analysis (RCA) is a widely used approach to retrospectively analyze safety events like surgical complications or medication administration errors. This article proposes RCA as an approach to analyzing diagnostic errors. While the five overarching steps of RCA for cases involving diagnostic error are similar to standard RCA (e.g., convening the appropriate team members), the authors detail important differences. System 1 and System 2 thinking, human factors, and cognitive biases are discussed. A related handbook provides detailed instructions for conducting an RCA on diagnostic errors.