This study investigates which factors predict whether consumers will pass on viral advertising communications to their friends on a social network site. A conceptual framework consisting of three attitudinal and three social predictors of forwarding online content was tested using three real-life advertising campaigns that were spread simultaneously through the Dutch social network site Hyves. Results show that viral advertising pass-on behavior was significantly predicted by a positive attitude toward the brand, the advertisement, and toward viral advertising in general. For two of the three advertisements participants were more likely to forward the advertisement when the advertisement was received from a friend rather than a company. The present study is the first to investigate the predictors of actual pass-on behavior of viral advertisements in the context of a social network site, thereby significantly contributing to existing knowledge on the drivers of viral advertising success.