The present study aimed to investigate Facebook Addiction Disorder (FAD) in a German student sample over a period of one year. While mean FAD level did not increase during the investigation period, a significant increase was shown in the number of participants reaching the critical cutoff score. FAD was significantly positively related to the personality trait narcissism and to negative mental health variables (depression, anxiety, and stress symptoms). Furthermore, FAD fully mediated the significant positive relationship between narcissism and stress symptoms, which demonstrates that narcissistic people can be specifically at risk to develop FAD. Present results give a first overview of FAD in Germany. Practical applications for future studies and limitations of present results are discussed.