Access to medical information via the Internet has the potential to speed the transformation of the patient-physician relationship from that of physician authority ministering advice and treatment to that of shared decision making between patient and physician. However, barriers impeding this transformation include wide variations in quality of content on the Web, potential for commercial interests to influence online content, and uncertain preservation of personal privacy. To address these issues, the American Medical Association (AMA) has developed principles to guide development and posting of Web site content, govern acquisition and posting of online advertising and sponsorship, ensure site visitors' and patients' rights to privacy and confidentiality, and provide effective and secure means of e-commerce. While these guidelines were developed for the AMA Web sites and visitors to these sites, they also may be useful to other providers and users of medical information on the Web. These principles have been developed with the understanding that they will require frequent revision to keep pace with evolving technology and practices on the Internet. The AMA encourages review and feedback from readers, Web site visitors, policymakers, and all others interested in providing reliable quality information via the Web.