Objectives: To test the hypothesis that weapon-related violence (excluding firearms) results in more severe injury relative to the use of body parts (fists, feet and other body parts), and to rank order of injury severity by assault mechanism. Design: Retrospective cohort study. Participants: 24 660 patients who were treated in a UK emergency department for violence-related injury. Main outcome measure: Score on the Manchester Triage Scale. Results: The use of a weapon resulted in significantly more serious injury (adjusted odds ratio (AOR) 1.13, 95% confidence interval (CI) 1.00 to 1.28). However, of all mechanisms of violent injury, the use of feet resulted in most severe injury (AOR 1.41, 95% CI 1.17 to 1.70), followed by blunt objects (AOR 1.35, 95% CI 1.14 to 1.58), other body parts (AOR 1.22, 95% CI 1.06 to 1.40) and sharp objects (AOR 1.09, 95% CI 0.91 to 1.5), compared with use of fists. Conclusions: Use of weapons resulted in more severe injury than use only of body parts. The use of feet caused the most serious injuries, whereas the use of fists caused the least severe injuries. Injury severity varied by number of assailants and age of the patient—peaking at 47 years—but not by number of injuries. Preventing the use of feet in violence, and preventing group violence should be major priorities.