Antimicrobial drug resistance is a significant cause of avoidable morbidity and mortality. Inappropriate prescribing of antimicrobials is acknowledged as a key determinant of this phenomenon. Many approaches are advocated for reducing this inappropriate prescribing, including regulatory, professional and educational interventions. Mass media campaigns are often suggested as a useful tool in managing public expectations, but the evidence to support this is weak, as no controlled studies of such campaigns exist. Evaluating such campaigns is problematic, and uncontrolled observations are misleading. We report here the first controlled study of such an intervention in the use of antimicrobials.Two sequential mass media campaigns, providing information on the appropriate use of antimicrobials, were conducted during early 2004 and 2005 in the North East of England. These messages were articulated in the campaign by the cartoon character 'Moxy Malone'. The campaigns were supported by printed materials, and in parts of this area, with professional education and prescribing support. A retrospective controlled before-after study was conducted, examining the effects on observed prescribing of antimicrobials for the populations covered by these two cycles of mass media campaigns. These populations were controlled with matched populations in the North of England. The primary outcome examined was prescribing rates (items) for all microbial agents for these populations, corrected for population structure (STAR-PU). A repeated measures analysis of variance (ANOVA) was used to analyse factors that had a possible effect on the prescribing of antibacterial drugs. This was supported by a survey of primary care organizations (PCOs) of all interventions undertaken around antimicrobial use in the intervention and comparison populations.In this retrospective study, there was incomplete reporting of adjuvant interventions undertaken by the PCOs intervention and comparison areas, so isolating the intervention, and attributing cause and effect is difficult. In this pragmatic evaluation the campaign was found to significantly reduce the volume of antibacterial drugs during the winter months of the intervention years. There were 21.7 fewer items prescribed per 1000 population (P < 0.0005), for the intervention populations over these winter months, equivalent to a 5.8% absolute reduction in prescribing.Mass media campaigns have a role in changing antimicrobial prescribing practice.