Background: We sought to determine the effects of becoming available online on impact factors of general medicine journals.

Methods: Through MEDLI NE with an institutional subscription, the 2004 online status of "Medicine, General and Internal" journals listed in the Institute for Scientific Information (ISI ) Journal Citation Reports (JCR) was classified as full text on the Net (FU TON), abstract only, or no abstract available (NAA)/unavailable in MEDLI NE. Similarly, through use of a home computer without an institutional subscription, the 2004 online status of the same journals was determined. For each journal, impact factors for 1992 to 2003 were obtained.

Results: Of the 102 "Medicine, General and Internal" journals listed in the ISI JCR, 71 (70%) existed in both pre-Internet (1992) and Internet (2003) eras. Of these 71 journals, those available as FU TON in 2004 had higher median impact factors than non-FU TON journals in 1992 (p < 0.0001> and 2003 (p < 0.0001). Journals that became available online, at least partially, had significant increases in median impact factors from 1992 to 2003 (p< 0.0001 for journals that became available as FUTON and for journals that provided an abstract only. However, journals that became available as FUTON had a greater increase in median impact from 1992 to 2003 than other journals (p = 0.002). Similar results were obtained using impact factor data according to journal online status through use of a home computer without an institutional subscription and for English-language journals only.

Conclusion: Becoming available online as FUTON is associated with a significant increase in journal impact factor.