Recent research has pointed to potential negative effects on young women of using social networking sites. We examined whether exposure to thin-idealised images of users' bodies, typical of those posted on Instagram, would result in changes in state mood and body dissatisfaction. We further examined women's reported thoughts when viewing such images to explore qualitatively their cognitive experiences. Female participants (N = 126) reported on trait body dissatisfaction and body comparison, and state body dissatisfaction and mood, and were randomly assigned to view and describe their thoughts about either images depicting the Western thin-ideal or control images (scenery). The control sample increased mood and decreased body dissatisfaction more than thin-ideal participants following exposure, with only marginal moderating effects of trait appearance comparison and internalization of the thin-ideal. In a sample that viewed the thin-ideal images (n = 91) upward body comparison thoughts and positive thoughts related to the bodies depicted were associated with negative mood changes. Media awareness and literacy thoughts were not protective; however, thoughts unrelated to the thin-ideal bodies were protective. Findings suggest that while young women appeared largely resilient to short-term exposure to Instagram images of thin-idealized peers, a subset of women appeared to be at risk.