This article describes the use of a new accident analysis technique (CAST, or Causal Analysis based on Systems Theory), an alternative approach to root cause analysis. The CAST approach is based on the principle that accidents are not only the result of individual system component failures or errors but more generally result due to inadequate enforcement of constraints on the behavior of the system components (i.e., safety constraints enforced by controls, such as checklists).  Many adverse events (AEs) appear to be related to the design of the system involved and not attributable to unsafe individual behavior. This technique can be useful in identifying causal factors to help health care systems learn from mistakes and design systems-level changes to prevent future AEs.