Personal profiles on social network sites have become an important tool for social evaluation – that is, assessing profile owners’ characteristics (e.g., personality traits, narcissism, physical and social attractiveness). The present study is one of the first to examine how users’ trustworthiness is evaluated by naïve observers based on information contained in Facebook profiles, or profile cues. Drawing on uncertainty reduction theory, warranting theory, and hardwired perceptions of facial displays, we propose a framework that identifies cues associated with trustworthiness in Facebook profiles. Results show that six profile cues (number of friends, number of tagged photographs, number of “about me” categories filled out, number of comments and “likes” received from friends, and smiling profile photographs) explained about a third of the variance in Facebook users’ perceived trustworthiness. Number of friends had a curvilinear, U-shaped effect on trustworthiness perceptions, with an inflection point at about 500 friends. That is, trustworthiness decreased as number of friends increased up to 500, and then trustworthiness increased as number of friends increased beyond 500. Theoretical and design implications of the findings are discussed.