Killed or seriously injured (KSI) is a standard metric for safety policy, particularly in transportation and road safety.

ISO 39001 considers a serious injury as one having an impact on the body or on the capacity of an individual.

The definitions used in the USA are as follows:

In 2014, 135,000 people were seriously injured on Europe's roads.

Figures for fatalities are normally highly reliable in industrialised countries, and few if any fatalities go unrecorded. Fatality figures are, however, often too low, making it hard to see trends over time for one place.

Figures for the number of people seriously injured typically are an order of magnitude larger than the number of people killed, and are therefore more likely to be statistically significant. However, classification of serious injuries is open to opinion, by medical staff or by non-medical professionals, such as police officers, and may therefore vary over time and between places.

Figures for slight injuries are considered highly unreliable, largely due to under-reporting where injuries are self-treated.

Several metrics are derived from KSI metrics, with various goals such as international comparisons which need normalization.