The Internet is a popular channel for health-related communication practices while trustworthiness of such information is a major determinant for health information seeking behaviors and intentions. This study examines the extent to which online health information discussion behaviors and sharing intentions are affected by the level of trust in health information from traditional sources, such as mass media and governmental agencies, as well as online sources, such as social media. An online survey was conducted in a large public university in Hong Kong. Trust in health information from traditional sources was found to associate positively with trust in online health information sources. In addition, an individual’s trust in online health information, particularly social media-based, was positively linked with his/her willingness to share health-related messages via the Internet. Moreover, trust in online health information mediated the relationship between trust in offline health information and one’s sharing intentions. In other words, while traditional health information sources are trustworthy, trust in traditional sources per se would not fully generate further health-related actions online unless one’s trust in online information is present.