In an effort to address healthcare disparities in lesbian, gay, bisexual, transgender, and queer (LGBTQ) populations, many hospitals and clinics institute diversity training meant to increase providers' awareness of and sensitivity to this patient population. Despite these efforts, many healthcare spaces remain inhospitable to LGBTQ patients and their loved ones. Even in the absence of overt forms of discrimination, LGBTQ patients report feeling anxious, unwelcome, ashamed, and distrustful in healthcare encounters. We argue that these negative experiences are produced by a variety of subtle, ostensibly insignificant features of healthcare spaces and interpersonal interactions called microaggressions. Healthcare spaces and providers often convey heteronormative microaggressions, which communicate to LGBTQ-and, we suggest, intersex and asexual (IA)-people that their identities, experiences, and relationships are abnormal, pathological, unexpected, unwelcome, or shameful. We identify heteronormative microaggressions common to healthcare settings and specify how they negatively impact LGBTQIA patients. We argue that standard diversity training cannot sufficiently address heteronormative microaggressions. Despite these challenges, healthcare institutions and providers must take responsibility for heteronormative microaggressions and take steps to reduce their frequency and mitigate their effects on LGBTQIA care. We conclude by offering strategies for problem-solving at the level of medical education, institutional culture and policy, and individual awareness.