Social media has become an increasingly popular leisure activity over the last decade. Although most people's social media use is non-problematic, a small number of users appear to engage in social media excessively and/or compulsively. The main objective of this study was to examine the associations between addictive use of social media, narcissism, and self-esteem. A cross-sectional convenient sample of 23,532 Norwegians (M age = 35.8 years; range = 16–88 years) completed an open web-based survey including the Bergen Social Media Addiction Scale (BSMAS), the Narcissistic Personality Inventory-16, and the Rosenberg Self-Esteem Scale. Results demonstrated that lower age, being a woman, not being in a relationship, being a student, lower education, lower income, lower self-esteem, and narcissism were associated with higher scores on the BSMAS, explaining a total of 17.5% of the variance. Although most effect sizes were relatively modest, the findings supported the notion of addictive social media use reflecting a need to feed the ego (i.e., narcissistic personality traits) and an attempt to inhibit a negative self-evaluation (i.e., self-esteem). The results were also consistent with demographic predictions and associations taken from central theories concerning “addiction”, indicating that women may tend to develop more addictive use of activities involving social interaction than men. However, the cross-sectional study design makes inferences about directionality impossible.