2010, Article / Letter to editor (Journal of Medical Internet Research, vol. 12, iss. 2, (2010), pp. e18)During the last decade, the Internet has become increasingly popular and is now an important part of our daily life. When new "Web 2.0" technologies are used in health care, the terms "Health 2.0" or "Medicine 2.0" may be used. The objective was to identify unique definitions of Health 2.0/Medicine 2.0 and recurrent topics within the definitions. A systematic literature review of electronic databases (PubMed, Scopus, CINAHL) and gray literature on the Internet using the search engines Google, Bing, and Yahoo was performed to find unique definitions of Health 2.0/Medicine 2.0. We assessed all literature, extracted unique definitions, and selected recurrent topics by using the constant comparison method.