Use of online social networking sites such as Facebook has burgeoned in the last 5 years. The authors examined these sites as facilitators of Online Obsessive Relational Intrusion (o-ORI)a much-talked about, but relatively un-researched online phenomenon. The authors draw parallels between the types of behaviors conducted online and those identified in the literature on relational intrusion and its more extreme relative, stalking. The authors present a frequency analysis of students' behavior on Facebook and find evidence of relational intrusion from both offenders and targets. The behaviors can be classified into five different categories, including: primary contact attempts, secondary contact attempts (i.e., contacting others connected to the target), monitoring or surveillance, expressions, and invitations. The authors conclude that Facebook facilitates behaviors that are indicative of obsessive relational intrusion and that such behaviors have implications for users' privacy and security. (Published Abstract)