Using a nationally-representative panel data set of U.S. high school students (AddHealth data) that contains a relatively large sample of siblings and twins, the paper investigates the impacts of gun availability at home and individual drug use on robbery, burglary, theft and damaging property for juveniles. Using a variety of fixed-effects models that exploit variations over time, the results show that gun availability at home increases the propensity to committing robbery, burglary and theft by about two percentage points for juveniles but has no impact on damaging property. It is unlikely that gun availability is merely a measure of the unobserved home environment because gun availability does not influence other risky or bad behaviors of juveniles. The results show that having access to guns increases the probability of being cut or stabbed by someone and of someone pulling a knife or gun on the juvenile. Estimates obtained from models that exploit variations over time and between siblings and twins indicate that the median impact of cocaine use on the propensity to commit various types of crimes is 23 percentage points. The impact of using inhalants or other drugs is an increase in the propensity to commit crime by 14 and 18 percentage points, respectively.