Study objective: I test the hypothesis that having a gun in the home is a risk factor for adults to be killed (homicide) or to commit suicide. Methods: Two case-control analyses were based on national samples of subjects 18 years of age or older. Homicide and suicide case subjects were drawn from the 1993 National Mortality Followback Survey. Living control subjects were drawn from the 1994 National Health Interview Survey. Ten control subjects matched by sex, race, and age group were sought for each case subject. Results: The homicide sample consisted of 1,720 case subjects and 8,084 control subjects. Compared with adults in homes with no guns, the adjusted odds ratio (OR) for homicide was 1.41 (95% confidence interval [CI] 1.20 to 1.65) for adults with a gun at home and was particularly high among women (adjusted OR 2.72; 95% CI 1.89 to 3.90) compared with men (adjusted OR 1.23; 95% CI 1.01 to 1.49) and among nonwhite subjects (adjusted OR 1.74; 95% CI 1.37 to 2.21) compared with white subjects (adjusted OR 1.27; 95% CI 1.03 to 1.56). Further analyses revealed that a gun in the home was a risk factor for homicide by firearm means (adjusted OR 1.72; 95% CI 1.40 to 2.12) but not by nonfirearm means (OR 0.83; 95% CI 0.62 to 1.11). The suicide sample consisted of 1,959 case subjects and 13,535 control subjects. The adjusted OR for suicide was 3.44 (95% CI 3.06 to 3.86) for persons with a gun at home. However, further analysis revealed that having a firearm in the home was a risk factor for suicide by firearm (adjusted OR 16.89; 95% CI 13.26 to 21.52) but was inversely associated with suicide by other means (adjusted OR 0.68; 95% CI 0.55 to 0.84). Conclusion: Having a gun at home is a risk factor for adults to be shot fatally (gun homicide) or commit suicide with a firearm. Physicians should continue to discuss with patients the implications of keeping guns at home. Additional studies are warranted to address study limitations and to better understand the implications of firearm ownership. [Ann Emerg Med. 2003;41:771-782.]