Chicago's CeaseFire program is an evidence-based public health approach to preventing gun violence. Baltimore is one of many US cities attempting to replicate the program. We compared changes in the number of homicide and nonfatal shooting incidents per month in four intervention neighborhoods with changes in high-crime comparison areas (police posts) without the intervention, while controlling for several measures of police activity and baseline levels of homicide and nonfatal shootings. In South Baltimore there were large program-related reductions in homicide and nonfatal shooting incidents. Among three East Baltimore program sites, the program was associated with a reduction of homicides in one area, a reduction in nonfatal shootings in another area, and a simultaneous increase in homicides and decrease in nonfatal shootings in another area. In some instances, program effects extended to neighborhoods bordering the intervention areas. Program-related reductions in homicides appear to be linked with conflict mediations conducted by program outreach workers.