Concerns have been raised regarding the extensive use of social media sites by young adults and adolescents and the effects this use may have on their mental health and general functioning. However, definitions of health are expansive and diverse. In the present article we assess 3 broad areas of mental and physical health: depressive symptoms, mindful attention, and physical symptoms. Additionally, the fear of missing out (FoMO), which relates to social media use both in its experience and origins, has received a great deal of popular attention recently with relatively less attention from researchers. In order to test the associations between social media use, FoMO, and a range of mental and physical health outcomes, an online study was conducted with 386 undergraduates from a large, ethnically diverse university. Results of this study demonstrated that FoMO was positively associated with time spent on social media. Furthermore, experiencing higher levels of FoMO was associated with more depressive symptoms, less mindful attention, and more physical symptoms. Moreover, time spent on social media was no longer related to depressive symptoms and mindful attention when FoMO was included in the model. Findings from this study suggest that FoMO may be a more revelatory measure than simple assessments of social media use, and is associated with negative health outcomes. (PsycINFO Database Record (c) 2016 APA, all rights reserved)