Background Violence is the fifth most common cause of death worldwide among 15–29 year olds; in 2004 there were more than 600 000 deaths worldwide caused by violence.

Methods Prompted by discoveries that a great deal of violence which results in emergency care is not ascertained by the police, a health service, police and local authority partnership was established in Cardiff to share emergency service data relevant to targeted prevention. Impact was assessed over 50 months using police records (more serious and less serious woundings, common assault), violence-related emergency department attendances in Cardiff and in Home Office designated most similar comparison cities. Socioeconomic conditions and adoption of a national crime recording standard in these cities were controlled for.

Findings The programme was associated with a substantial and significant reduction in wounding (by approximately 100 per month by month 50; 95% CI 940 to 1070) and in emergency department attendances (by approximately 30 per month; 95% CI 235 to 375) and with a significant increase in common assaults (by approximately 35 per month (95% CI 287 to 410). Interpretation This programme is associated with reduced violence both from a police and emergency department perspective. The principal mechanism is likely to be more frequent and earlier police intervention consequent upon better targeted policing than is achievable using police data alone.