There is widespread unawareness and disbelief regarding the evidence-based conclusion that people who have a sustained undetectable HIV viral load cannot sexually transmit HIV-ie, undetectable=untransmittable (U=U). Long-standing, misguided fear about HIV transmission persists; consequently, so does the policing of sexual expression and the penalisation of pleasure faced by people with HIV. Many people with HIV with an undetectable viral load have unnecessarily abstained from condomless sex, avoided serodifferent partnering, and had anxiety about onward sexual transmission due to perceived HIV risk that is now known to be non-existent. Some health professionals have refrained from correcting this misinformation because of concerns that people with HIV will engage in more condomless sex or have more sexual partners upon learning of U=U. Withholding information about U=U is thus rooted in behavioural assumptions and is scientifically unfounded. Moreover, withholding such information violates medical ethics, perpetuates health inequities, and infringes on the sexual health and human rights of people with HIV. Health professionals and the broader public health community have an ethical responsibility to actively address misinformation about HIV transmission and disseminate the U=U message to all people.