This study evaluated the quality of Web-based information on cannabis use and addiction and investigated particular content quality indicators. Three keywords ("cannabis addiction," "cannabis dependence," and "cannabis abuse") were entered into two popular World Wide Web search engines. Websites were assessed with a standardized proforma designed to rate sites on the basis of accountability, presentation, interactivity, readability, and content quality. "Health on the Net" (HON) quality label, and DISCERN scale scores were used to verify their efficiency as quality indicators. Of the 94 Websites identified, 57 were included. Most were commercial sites. Based on outcome measures, the overall quality of the sites turned out to be poor. A global score (the sum of accountability, interactivity, content quality and esthetic criteria) appeared as a good content quality indicator. While cannabis education Websites for patients are widespread, their global quality is poor. There is a need for better evidence-based information about cannabis use and addiction on the Web.