This observational study compared the implementation of the WHO Surgical Safety Checklist at a hospital in New Zealand with a neighboring hospital that had served as a pilot site for the study. They found that the pilot hospital adhered to the sign in, time out, and sign out procedures of the checklist more frequently than the hospital that adopted the checklist outside the context of a study. The non-pilot site did have engagement across more disciplines (anesthesia, surgery, nursing), compared with the nurse-only engagement at the pilot hospital. These findings shed light on the difficulty of implementing safety practices widely.