In 2002, the Baltimore City Health Department, in collaboration with the Baltimore Police Department and the Johns Hopkins Center for Gun Policy and Research, launched the Youth Ammunition Initiative. The initiative addressed Baltimore's problem of youth gun violence by targeting illegal firearm ammunition sales to the city's young people. The initiative included undercover "sting" investigations of local businesses and issuance of health department violation and abatement notices. Intermediate results included the passage of 2 Baltimore city council ordinances regulating ammunition sales and reducing the number of outlets eligible to sell ammunition. Although it is too early to assess effects on violent crime, the intervention could theoretically reduce youth violence by interrupting one source of ammunition to youths. More important, the initiative can serve as a policy model for health commissioners seeking to become more active in gun violence prevention efforts.