This study used recently released nationally representative data with new measures on health information seeking to estimate the prevalence and predictors of adult social media users’ perceptions of health mis- and disinformation on social media. Most adults who use social media perceive some (46%) or a lot (36%) of false or misleading health information on social media, but nearly a fifth reported either none or a little (18%). More than two-thirds of participants reported that they were unable to assess social media information as true or false (67%). Our study identified certain population groups that might be a focus of future intervention work such as participants who use social media to make decisions. The perception by social media users that false and misleading health information on social media is highly prevalent may lend greater urgency to mitigate the spread of false or misleading health information that harms public health.