This study describes how Swedish authorities handle medical errors reported by health care providers, and also describes effects on the willingness to report medical errors. The Swedish self-reporting system for medical errors focuses on serious injuries caused by treatment in the health care sector and has its origin in an incident that occurred in 1936 at the Maria Hospital in Stockholm (Ödegård and Löfroth, 1996). Four patients died following injection of mercuric oxicyanide instead of a local anesthetic. The first law in 1937 focused on disciplinary action, assigning the duty to report patient injuries to both the National Board of Health and Welfare (NBHW) and the police. The regulation (called lex Maria) has been changed over the past 60 years, as has the manner in which the NBHW handles lex Maria cases. The focus has changed from having a disciplinary aim, where the issue was to determine guilt, to the aim of prevention. In connection with a reorganization of the NBHW in 1991, a variety of measures were adopted in order to widen the scope of prevention in the area of patient injuries caused by medical treatment. Extensive information was distributed to health care personnel in order to achieve a better understanding of the importance of reporting medical errors.