A recent study has shown that over two-thirds of Facebook users have posted at least one health-related post on Facebook in the past year including health information or posts about a health condition or health-related behavior. Facebook allows users to create groups where users can discuss specific topics. Health-related groups abound on Facebook and studies have shown that patients benefit from sharing their experiences with other patients in these groups. Little is known about the prevalence of Facebook health-related group membership among Facebook users and the characteristics of users in health-related Facebook groups. We conducted a cross-sectional survey of 2,508 US adult Facebook users to determine the (a) proportion of users in Facebook groups who belong to health-related Facebook groups, (b) proportion of users whose most paid attention to Facebook group was a health group, and (c) user characteristics associated with health-related group membership including age, gender, race/ethnicity, education, income, and chronic disease status. Of the Facebook users surveyed (N=2,508; 74.7% female; mean age=40.89 SD=15.02), 74.5% belonged to at least one Facebook group. Of those, 34.2% belonged to a health-related Facebook group. About 9.1% of those who belonged to Facebook groups indicated that the Facebook group they paid the most attention to was a health-related group. Using multivariate logistic regression, we found that Facebook users with college degrees had higher odds of belonging to a health-related group compared to those with high school education or less. Facebook users who had chronic disease had higher odds of belonging to a health-related group on Facebook compared to those who did not. Age, gender, race/ethnicity, and household income were not associated with health-related Facebook group membership. Future research should investigate the psychosocial and health-related benefits of being a member of and/or engaging in health-related Facebook groups.