The use of Internet references in academic literature is common, and Internet references are frequently inaccessible. The extent of Internet referencing and Internet reference activity in medical or scientific publications was systematically examined in more than 1000 articles published between 2000 and 2003 in the New England Journal of Medicine, The Journal of the American Medical Association, and Science. Internet references accounted for 2.6% of all references (672/25548) and in articles 27 months old, 13% of Internet references were inactive. Publishers, librarians, and readers need to reassess policies, archiving systems, and other resources for addressing Internet reference attrition to prevent further information loss.