Objectives: (1) To quantify lethality of firearms relative to other suicide methods, (2) to quantify the extent to which suicide mortality may be reduced by limiting access to firearms.

Methods: Data on suicides and hospitalised para-suicides that occurred in the state of Illinois from 1990 to 1997 were combined. Total number of episodes for each suicide method was estimated as the sum of the number of suicides and the number of para-suicides for that method. Gender and suicide method were used as proxies for intention to die, and estimated lethality of suicide methods within method-gender groups (for example, male firearm users). Logistic regression was used to quantify the lethality of firearms relative to other suicide methods. Excess mortality associated with the use of firearms was estimated by conservatively assuming that in the absence of firearms the next most lethal suicide method would be used.

Results: From January 1990 to December 1997, among individuals 10 years or older in the state of Illinois, there were 37 352 hospital admissions for para-suicide and 10 287 completed suicides. Firearms are the most lethal suicide method. Episodes involving firearms are 2.6 times (95% CI 2.1 to 3.1) more lethal than those involving suffocation—the second most lethal suicide method. Preventing access to firearms can reduce the proportion of fatal firearms related suicides by 32% among minors, and 6.5% among adults.

Conclusions: Limiting access to firearms is a potentially effective means of reducing suicide mortality.