A meta-analysis was performed of studies of mediated health campaigns in the United States in order to examine the effects of the campaigns on behavior change. Mediated health campaigns have small measurable effects in the short-term. Campaign effect sizes varied by the type of behavior: r=.15 for seat belt use, r=.13 for oral health, r=.09 for alcohol use reduction, r=.05 for heart disease prevention, r=.05 for smoking, r=.04 for mammography and cervical cancer screening, and r=.04 for sexual behaviors. Campaigns with an enforcement component were more effective than those without. To predict campaign effect sizes for topics other than those listed above, researchers can take into account whether the behavior in a cessation campaign was addictive, and whether the campaign promoted the commencement of a new behavior, versus cessation of an old behavior, or prevention of a new undesirable behavior. Given the small campaign effect sizes, campaign planners should set modest goals for future campaigns. The results can also be useful to evaluators as a benchmark for campaign effects and to help estimate necessary sample size.