DescriptionHeterosexual men may avoid caring for their health due to the fear that they will experience a masculinity threat and be misperceived as gay or experience stigma-by-association. Across three studies, how the fear of being misperceived as gay and stigma-by-association influence men’s health behavior was examined using the theory of planned behavior (TPB) as a theoretical guide. Study 1 examined the extent to which attitudes, descriptive and injunctive norms, and perceived behavioral control predict heterosexual men’s health-promoting and risky health behaviors when a health intervention made gender and sexual orientation salient through targeting an exclusively heterosexual male audience or a male audience varying in sexual orientation. While the hypothesized model using the TPB framework did not fit the data, exploratory models suggested that descriptive norms for sexual orientation (i.e., how comparatively common performing health behaviors is perceived to be among heterosexual and gay persons) influenced heterosexual men’s health behaviors. Study 2 examined whether heterosexual men risk having their sexual orientation misperceived or becoming targets of stigma-by-association when seeking care from medical professionals who vary by sexual orientation (gay, heterosexual) and occupation (nurse practitioner, psychiatrist, personal trainer), and explored how potential stigmatization of men seeking care may result due to sexual orientation injunctive and descriptive norms. When seeking care from medical professionals was perceived as more common among gay rather than heterosexual men (i.e., descriptive sexual orientation norms were comparatively low for heterosexual men), men seeking care were perceived as less likely to be heterosexual, suggesting that misperceptions of sexual orientation may occur for heterosexual men engaging in specific healthcare seeking behaviors. In Study 3, the source of information expressing norms for men’s health behavior (i.e., heterosexual medical provider, gay medical provider) was manipulated to further examine how fear of being misperceived as gay and stigma-by-association may alter health behavioral intentions among heterosexual men. The greater heterosexual men’s stigma-by-association concerns, the less willing they were to adhere to health behavior recommendations from a medical provider. The results of these three studies inform understanding of how health-promoting behaviors can be encouraged and risky health behaviors discouraged among heterosexual men. Exploring how stigma functions in a healthcare setting may provide insight into how to intervene to improve the lives of not only those concerned about stigma-by-association but also those who experience stigmatization firsthand.