This research examines the effectiveness of the myth/fact message format (MFMF)—a message format that first presents a common misperception as a myth then counters it with a correcting fact—within the health-care and social marketing context of mental illness (MI). Stereotype processing theory predicts that the use of a negative aspect of the stereotype in a MFMF may further instantiate the negative belief, thereby reducing the effectiveness of the message. Conversely, using a message format that conveys only facts (i.e., new positive beliefs) without inclusion of the myth will lead to more positive attitudes. However, this effect will only be seen among people with personal relevance with MI as only they are sufficiently motivated to suppress the automatically activated stereotype and elaborate on the message. A study demonstrates that advertising utilizing a fact-only format leads to more positive attitudes than the MFMF among people with personal relevance while people without personal relevance to MI demonstrate no differences in attitude between myth/fact and fact-only message formats. Personal relevance had the opposite moderating effect on perceived learning. These findings suggest that the MFMF's impact on attitudes, the typical focal point of social marketing campaigns targeting misconceptions about stereotyped groups, may be ineffective. Thus, using a fact-only format that conveys new positive beliefs in a social marketing message is recommended within the specific context of MI and may be warranted in other health-care and social issues.