The Swedish system concerning injuries in the health care sector has its origin in an incident 1936 at the Maria hospital in Stockholm. Four patients died following injection of mercury oxycyanide instead of a local anaesthetic. The first law in 1937 focused on disciplinary actions with prescribed duties to report patient injuries both to the National Board of Health and Welfare and the local police. The regulations, often called lex Maria, have changed during the past 60 years. It is now stressed, beside the punitive aspects, that also incidents not causing injuries should be reported, that organisational factors should be considered in the evaluations of incidents and that a main aspect of the system is prevention.