BACKGROUND: In the United States, more people kill themselves with firearms than with all other methods combined. A central question regarding the relation between firearms and suicide is whether the ready availability of firearms increases the suicide rate, rather than merely increasing the proportion of suicides from guns. METHODS: We used publicly available data for the nine regions and 50 states in the United States over a 10-year period (1988-1997) to examine the association between levels of household firearm ownership and rates of suicide, firearm suicide, and non-firearm suicide by age groups and gender. RESULTS: In both regional and state-level analyses, for the U.S. population as a whole, for both males and females, and for virtually every age group, a robust association exists between levels of household firearm ownership and suicide rates. CONCLUSIONS: Where firearm ownership levels are higher, a disproportionately large number of people die from suicide.