To examine the association between carrying a weapon at school and the age of onset of substance use, other indicators of violence, and other health risk behaviors among middle school students. In 1995, a modified version of the Centers for Disease Control and Prevention Youth Risk Behavior Survey was administered to 2227 students (49% were female) attending 53 (of 463) randomly selected middle schools in North Carolina. Weapon carrying on school property during school hours was measured with 2 questions assessing carrying a gun and carrying other weapons such as knives or clubs. The Youth Risk Behavior Survey also assessed other indicators of violence, drug use, suicide plans and attempts, and being threatened with a weapon at school. Variables significantly (P< or =.001) associated with gun and other weapon carrying by chi2 tests were analyzed with stepwise logistic regression using the likelihood ratio approach. Odds ratios (ORs) were adjusted for all other variables in the model and 95% confidence intervals (CIs) were computed. Our study showed that 3% of students had carried a gun and 14.1% had carried a knife or club to school. Gun carrying was associated with increased age (OR, 1.57 [95% CI, 1.15-2.14]); male sex (OR, 5.62 [95% CI, 2.42-13.03]); minority ethnicity (OR, 3.30 [95% CI, 1.55-5.05]); and earlier age of onset of cigarette (OR, 0.85 [95% CI, 0.74-0.97]), alcohol (OR, 0.81 [95% CI, 0.71-0.94]), marijuana (OR, 0.81 [95% CI, 0.71-0.92]), and cocaine use (OR, 0.73 [95% CI, 0.62-0.86]). Knife or club carrying was associated with age (OR, 1.32 [95% CI, 1.14-1.53]); male sex (OR, 2.39 [95% CI, 1.77-2.32]); and ear-lier age of onset of cigarette (OR, 0.88 [95% CI, 0.84-0.94]), alcohol (OR, 0.81 [95% CI, 0.76-0.86]), and marijuana use (OR, 0.77 [95% CI, 0.72-0.83]). Gun carrying was also associated with frequency of cigarette (OR, 1.34 [95% CI, 1.14-1.57]), alcohol (OR, 4.59 [95% CI, 1.27-16.58]), cocaine (OR, 2.96 [95% CI, 1.29-6.82]), and marijuana use (OR, 3.66 [95% CI, 1.67-8.06]) after adjusting for male sex and minority ethnicity. Carrying a knife or club was associated with carrying a gun (OR, 1.83 [95% CI, 1.31-2.55]); being threatened with a weapon at school (OR, 1.65 [95% CI, 1.10-2.49]); fighting (OR, 4.62 [95% CI, 2.56-8.37]); frequency of alcohol (OR, 2.91 [95% CI, 1.88-4.50]) and cigarette use (OR, 1.20 [95% CI, 1.10-1.31]); and a suicide plan (OR, 1.54 [95% CI, 1.07-2.20]). Middle school students are more likely to carry a knife or club (14.1%) than a gun (3%) to school. Young adolescents who initiate substance use early and engage in it frequently are more likely to carry guns and other weapons to school, after adjusting for age, sex, and ethnicity. Being threatened with a weapon at school and fighting were only associated with knife or club carrying at school. These findings suggest that school-based prevention programs targeting both violence prevention and substance use should be introduced in elementary school.