To establish reliable quality criteria for medical websites is of foremost importance in relation to the increasing number of Internet users, both health professionals and lay people, searching for medical information in the mass of these sites. Quality in general refers to a set of features that distinguish one person or thing from others of the same type. The quality of a website is usually related to its content and usability. The first criteria we considered are contents and readability, which must be targeted to the intended type of user. Other important criteria include: transparency, consistency, honesty, references to sources, accountability, respect of privacy, currency of content material, responsibility, and accessibility. Technical criteria are the use of consolidated and standard technologies, soft colours, short page download time. Good medical websites should also follow the suggestions of organizations such as the World Health Organization, the Food and Drug Administration, the European Communities. Another organization, Health On Net Foundation, has issued some guidelines for medical websites, summarized in eight points, fundamental to assign real scientific value to a site. We believe, in agreement with the literature, that it is unnecessary to apply strict rules to medical website developers. We want to stress the importance of guidelines and recommendations to be modified with the development of web technology and the cultural evolution of patient and physicians. In the near future the presence on the Internet of websites certified by national or international medical web authorities will lead users to trust and give their preference to such sites, leading to the self-regulation of website developers and users.