For people with narcissistic qualities, Buffardi said, social networking sites are effective vehicles of self-promotion. Online, they can assemble armies of casual friends, choose the photos in which they look most attractive and, through quotes and comments about themselves, create a compelling personal narrative.

As social networking sites gain traction among greater swaths of the population -- Facebook now has more than 100 million members -- psychologists are becoming increasingly interested in how personality traits are expressed on the Internet. This study was one of the first attempts to achieve that. "These sites, like MySpace and Facebook, are becoming vastly popular. Lots of individuals are posting information about themselves and some psychologists have wanted to determine how narcissism manifests itself on Facebook," Buffardi said, adding that her study focused on narcissism as a trait, not a clinical disorder.

People identified as narcissistic in this study may have inflated views of themselves, she said. But they don't necessarily need to seek therapy for what can be a severe personality disorder. Buffardi and Campbell were particularly interested in narcissism because, while it may find expression online, it can hinder the creation of healthy relationships offline.

Wendy Behary, a narcissism expert and the author of "Disarming the Narcissist," told ABCNews.com that Facebook allows narcissists to remain disconnected from true intimacy and maintain a lack of accountability. They may look like they have a ton of friends, but they're actually affiliates, or awestruck followers, she said.

"At the core of most people who are narcissistic, underneath they often feel inadequate, lonely [and] a sense of shame because they haven't learned the skills to connect with someone in a real way," she said. "Facebook allows them to stay in hiding."

In addition to finding that people who score higher on narcissism personality tests tend to have more friends and wall posts on Facebook, the study also noted that they chose more glamorous photographs.